diff --git a/lib/systems/doubles.nix b/lib/systems/doubles.nix
index 96e602d0e16..619b0427918 100644
--- a/lib/systems/doubles.nix
+++ b/lib/systems/doubles.nix
@@ -26,7 +26,13 @@ let
 
     "riscv32-linux" "riscv64-linux"
 
-    "aarch64-none" "avr-none" "arm-none" "i686-none" "x86_64-none" "powerpc-none" "msp430-none" "riscv64-none" "riscv32-none" "vc4-none"
+    "arm-none" "armv6l-none" "aarch64-none"
+    "avr-none"
+    "i686-none" "x86_64-none"
+    "powerpc-none"
+    "msp430-none"
+    "riscv64-none" "riscv32-none"
+    "vc4-none"
 
     "js-ghcjs"
   ];
diff --git a/lib/tests/systems.nix b/lib/tests/systems.nix
index 6f52912994d..dd2b9575fc2 100644
--- a/lib/tests/systems.nix
+++ b/lib/tests/systems.nix
@@ -14,7 +14,7 @@ let
 in with lib.systems.doubles; lib.runTests {
   testall = mseteq all (linux ++ darwin ++ freebsd ++ openbsd ++ netbsd ++ illumos ++ wasi ++ windows ++ embedded ++ js);
 
-  testarm = mseteq arm [ "armv5tel-linux" "armv6l-linux" "armv7a-linux" "armv7l-linux" "arm-none" "armv7a-darwin" ];
+  testarm = mseteq arm [ "armv5tel-linux" "armv6l-linux" "armv6l-none" "armv7a-linux" "armv7l-linux" "arm-none" "armv7a-darwin" ];
   testi686 = mseteq i686 [ "i686-linux" "i686-freebsd" "i686-netbsd" "i686-openbsd" "i686-cygwin" "i686-windows" "i686-none" "i686-darwin" ];
   testmips = mseteq mips [ "mipsel-linux" ];
   testx86_64 = mseteq x86_64 [ "x86_64-linux" "x86_64-darwin" "x86_64-freebsd" "x86_64-openbsd" "x86_64-netbsd" "x86_64-cygwin" "x86_64-solaris" "x86_64-windows" "x86_64-none" ];
diff --git a/pkgs/build-support/cc-wrapper/default.nix b/pkgs/build-support/cc-wrapper/default.nix
index 7ae1c87e993..96d48ecbc79 100644
--- a/pkgs/build-support/cc-wrapper/default.nix
+++ b/pkgs/build-support/cc-wrapper/default.nix
@@ -10,7 +10,7 @@
 , cc ? null, libc ? null, bintools, coreutils ? null, shell ? stdenvNoCC.shell
 , nativeTools, noLibc ? false, nativeLibc, nativePrefix ? ""
 , propagateDoc ? cc != null && cc ? man
-, extraPackages ? [], extraBuildCommands ? ""
+, extraTools ? [], extraPackages ? [], extraBuildCommands ? ""
 , isGNU ? false, isClang ? cc.isClang or false, gnugrep ? null
 , buildPackages ? {}
 , libcxx ? null
@@ -214,7 +214,7 @@ stdenv.mkDerivation {
     '';
 
   strictDeps = true;
-  propagatedBuildInputs = [ bintools ];
+  propagatedBuildInputs = [ bintools ] ++ extraTools;
   depsTargetTargetPropagated = extraPackages;
 
   wrapperName = "CC_WRAPPER";
diff --git a/pkgs/development/compilers/llvm/5/default.nix b/pkgs/development/compilers/llvm/5/default.nix
index 05f4dbf6aa0..3c1b07e7ca7 100644
--- a/pkgs/development/compilers/llvm/5/default.nix
+++ b/pkgs/development/compilers/llvm/5/default.nix
@@ -23,7 +23,7 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString stdenv.targetPlatform.isLinux ''
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
       echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
     '';
   in {
@@ -50,8 +50,10 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      extraPackages = [
+      extraTools = [
         libstdcxxHook
+      ];
+      extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
       extraBuildCommands = mkExtraBuildCommands cc;
diff --git a/pkgs/development/compilers/llvm/6/default.nix b/pkgs/development/compilers/llvm/6/default.nix
index d4745930ed3..ba704f972c3 100644
--- a/pkgs/development/compilers/llvm/6/default.nix
+++ b/pkgs/development/compilers/llvm/6/default.nix
@@ -23,7 +23,7 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString stdenv.targetPlatform.isLinux ''
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
       echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
     '';
   in {
@@ -50,8 +50,10 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      extraPackages = [
+      extraTools = [
         libstdcxxHook
+      ];
+      extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
       extraBuildCommands = mkExtraBuildCommands cc;
diff --git a/pkgs/development/compilers/llvm/7/compiler-rt.nix b/pkgs/development/compilers/llvm/7/compiler-rt.nix
index ae98940adea..7a5e3d4c8fc 100644
--- a/pkgs/development/compilers/llvm/7/compiler-rt.nix
+++ b/pkgs/development/compilers/llvm/7/compiler-rt.nix
@@ -1,4 +1,13 @@
 { stdenv, version, fetch, cmake, python3, llvm, libcxxabi }:
+
+let
+
+  useLLVM = stdenv.hostPlatform.useLLVM or false;
+  bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  inherit (stdenv.hostPlatform) isMusl;
+
+in
+
 stdenv.mkDerivation {
   pname = "compiler-rt";
   inherit version;
@@ -11,26 +20,34 @@ stdenv.mkDerivation {
     "-DSCUDO_DEFAULT_OPTIONS=DeleteSizeMismatch=0:DeallocationTypeMismatch=0"
   ];
 
-  cmakeFlags = stdenv.lib.optionals (stdenv.hostPlatform.useLLVM or false || stdenv.isDarwin) [
+  cmakeFlags = stdenv.lib.optionals (useLLVM || stdenv.isDarwin) [
     "-DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON"
     "-DCMAKE_C_COMPILER_TARGET=${stdenv.hostPlatform.config}"
     "-DCMAKE_ASM_COMPILER_TARGET=${stdenv.hostPlatform.config}"
-  ] ++ stdenv.lib.optionals (stdenv.hostPlatform.useLLVM or false) [
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
-    "-DCMAKE_CXX_COMPILER_WORKS=ON"
-    "-DCOMPILER_RT_BUILD_BUILTINS=ON"
+  ] ++ stdenv.lib.optionals (useLLVM || bareMetal || isMusl) [
     "-DCOMPILER_RT_BUILD_SANITIZERS=OFF"
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
+  ] ++ stdenv.lib.optionals (useLLVM || bareMetal) [
+    "-DCMAKE_C_COMPILER_WORKS=ON"
+    "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
+    "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ stdenv.lib.optionals (useLLVM) [
+    "-DCOMPILER_RT_BUILD_BUILTINS=ON"
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
+    #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
+    "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
+  ] ++ stdenv.lib.optionals (bareMetal) [
+    "-DCOMPILER_RT_OS_DIR=baremetal"
   ];
 
   outputs = [ "out" "dev" ];
 
   patches = [
     ./compiler-rt-codesign.patch # Revert compiler-rt commit that makes codesign mandatory
-  ] ++ stdenv.lib.optional (stdenv.hostPlatform.useLLVM or false) ./crtbegin-and-end.patch
+  ] ++ stdenv.lib.optional (useLLVM) ./crtbegin-and-end.patch
     ++ stdenv.lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch;
 
   # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
@@ -41,7 +58,7 @@ stdenv.mkDerivation {
   postPatch = stdenv.lib.optionalString stdenv.isDarwin ''
     substituteInPlace cmake/config-ix.cmake \
       --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
-  '' + stdenv.lib.optionalString (stdenv.hostPlatform.useLLVM or false) ''
+  '' + stdenv.lib.optionalString (useLLVM) ''
     substituteInPlace lib/builtins/int_util.c \
       --replace "#include <stdlib.h>" ""
     substituteInPlace lib/builtins/clear_cache.c \
@@ -53,7 +70,7 @@ stdenv.mkDerivation {
   # Hack around weird upsream RPATH bug
   postInstall = stdenv.lib.optionalString stdenv.isDarwin ''
     ln -s "$out/lib"/*/* "$out/lib"
-  '' + stdenv.lib.optionalString (stdenv.hostPlatform.useLLVM or false) ''
+  '' + stdenv.lib.optionalString (useLLVM) ''
     ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/linux/crtbegin.o
     ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/linux/crtend.o
     ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/linux/crtbeginS.o
diff --git a/pkgs/development/compilers/llvm/7/default.nix b/pkgs/development/compilers/llvm/7/default.nix
index 04e1610fb79..5124a5df00b 100644
--- a/pkgs/development/compilers/llvm/7/default.nix
+++ b/pkgs/development/compilers/llvm/7/default.nix
@@ -23,7 +23,7 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc) ''
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
       echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
     '';
   in {
@@ -57,8 +57,10 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      extraPackages = [
+      extraTools = [
         libstdcxxHook
+      ];
+      extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
       extraBuildCommands = mkExtraBuildCommands cc;
diff --git a/pkgs/development/compilers/llvm/8/compiler-rt.nix b/pkgs/development/compilers/llvm/8/compiler-rt.nix
index 9c0829146f7..795c81f4219 100644
--- a/pkgs/development/compilers/llvm/8/compiler-rt.nix
+++ b/pkgs/development/compilers/llvm/8/compiler-rt.nix
@@ -1,4 +1,13 @@
 { stdenv, version, fetch, cmake, python3, llvm, libcxxabi }:
+
+let
+
+  useLLVM = stdenv.hostPlatform.useLLVM or false;
+  bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  inherit (stdenv.hostPlatform) isMusl;
+
+in
+
 stdenv.mkDerivation {
   pname = "compiler-rt";
   inherit version;
@@ -11,27 +20,26 @@ stdenv.mkDerivation {
     "-DSCUDO_DEFAULT_OPTIONS=DeleteSizeMismatch=0:DeallocationTypeMismatch=0"
   ];
 
-  cmakeFlags = stdenv.lib.optionals (stdenv.hostPlatform.useLLVM or false) [
+  cmakeFlags = stdenv.lib.optionals (useLLVM || stdenv.isDarwin) [
     "-DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON"
     "-DCMAKE_C_COMPILER_TARGET=${stdenv.hostPlatform.config}"
     "-DCMAKE_ASM_COMPILER_TARGET=${stdenv.hostPlatform.config}"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
-    "-DCMAKE_CXX_COMPILER_WORKS=ON"
+  ] ++ stdenv.lib.optionals (useLLVM || bareMetal || isMusl) [
     "-DCOMPILER_RT_BUILD_SANITIZERS=OFF"
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
+  ] ++ stdenv.lib.optionals (useLLVM || bareMetal) [
+    "-DCMAKE_C_COMPILER_WORKS=ON"
+    "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
+    "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ stdenv.lib.optionals (useLLVM) [
+    "-DCOMPILER_RT_BUILD_BUILTINS=ON"
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
-    "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
-  ] ++ stdenv.lib.optionals stdenv.hostPlatform.isMusl [
-    "-DCOMPILER_RT_BUILD_SANITIZERS=OFF"
-    "-DCOMPILER_RT_BUILD_XRAY=OFF"
-    "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
-    "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ stdenv.lib.optionals (stdenv.hostPlatform.parsed.kernel.name == "none") [
-    "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
+  ] ++ stdenv.lib.optionals (bareMetal) [
     "-DCOMPILER_RT_OS_DIR=baremetal"
   ];
 
@@ -40,7 +48,7 @@ stdenv.mkDerivation {
   patches = [
     ./compiler-rt-codesign.patch # Revert compiler-rt commit that makes codesign mandatory
   ]# ++ stdenv.lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch
-    ++ stdenv.lib.optional (stdenv.hostPlatform.useLLVM or false) ./crtbegin-and-end.patch;
+    ++ stdenv.lib.optional (useLLVM) ./crtbegin-and-end.patch;
 
   # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
   # to get it, but they're unfree. Since LLVM is rather central to the stdenv, we patch out TSAN support so that Hydra
@@ -50,7 +58,7 @@ stdenv.mkDerivation {
   postPatch = stdenv.lib.optionalString stdenv.isDarwin ''
     substituteInPlace cmake/config-ix.cmake \
       --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
-  '' + stdenv.lib.optionalString (stdenv.hostPlatform.useLLVM or false) ''
+  '' + stdenv.lib.optionalString (useLLVM) ''
     substituteInPlace lib/builtins/int_util.c \
       --replace "#include <stdlib.h>" ""
     substituteInPlace lib/builtins/clear_cache.c \
@@ -62,7 +70,7 @@ stdenv.mkDerivation {
   # Hack around weird upsream RPATH bug
   postInstall = stdenv.lib.optionalString (stdenv.hostPlatform.isDarwin || stdenv.hostPlatform.isWasm) ''
     ln -s "$out/lib"/*/* "$out/lib"
-  '' + stdenv.lib.optionalString (stdenv.hostPlatform.useLLVM or false) ''
+  '' + stdenv.lib.optionalString (useLLVM) ''
     ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbegin.o
     ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/crtend.o
     ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
diff --git a/pkgs/development/compilers/llvm/8/default.nix b/pkgs/development/compilers/llvm/8/default.nix
index d604dda5fe5..105011595c8 100644
--- a/pkgs/development/compilers/llvm/8/default.nix
+++ b/pkgs/development/compilers/llvm/8/default.nix
@@ -57,8 +57,10 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      extraPackages = [
+      extraTools = [
         libstdcxxHook
+      ];
+      extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
       extraBuildCommands = mkExtraBuildCommands cc;
diff --git a/pkgs/development/compilers/llvm/9/compiler-rt.nix b/pkgs/development/compilers/llvm/9/compiler-rt.nix
index 037953bb23d..0cfd8d7c9e7 100644
--- a/pkgs/development/compilers/llvm/9/compiler-rt.nix
+++ b/pkgs/development/compilers/llvm/9/compiler-rt.nix
@@ -1,4 +1,13 @@
 { stdenv, version, fetch, cmake, python3, llvm, libcxxabi }:
+
+let
+
+  useLLVM = stdenv.hostPlatform.useLLVM or false;
+  bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  inherit (stdenv.hostPlatform) isMusl;
+
+in
+
 stdenv.mkDerivation rec {
   pname = "compiler-rt";
   inherit version;
@@ -11,27 +20,26 @@ stdenv.mkDerivation rec {
     "-DSCUDO_DEFAULT_OPTIONS=DeleteSizeMismatch=0:DeallocationTypeMismatch=0"
   ];
 
-  cmakeFlags = stdenv.lib.optionals (stdenv.hostPlatform.useLLVM or false) [
+  cmakeFlags = stdenv.lib.optionals (useLLVM || stdenv.isDarwin) [
     "-DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON"
     "-DCMAKE_C_COMPILER_TARGET=${stdenv.hostPlatform.config}"
     "-DCMAKE_ASM_COMPILER_TARGET=${stdenv.hostPlatform.config}"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
-    "-DCMAKE_CXX_COMPILER_WORKS=ON"
+  ] ++ stdenv.lib.optionals (useLLVM || bareMetal || isMusl) [
     "-DCOMPILER_RT_BUILD_SANITIZERS=OFF"
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
+  ] ++ stdenv.lib.optionals (useLLVM || bareMetal) [
+    "-DCMAKE_C_COMPILER_WORKS=ON"
+    "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
+    "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ stdenv.lib.optionals (useLLVM) [
+    "-DCOMPILER_RT_BUILD_BUILTINS=ON"
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
-    "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
-  ] ++ stdenv.lib.optionals stdenv.hostPlatform.isMusl [
-    "-DCOMPILER_RT_BUILD_SANITIZERS=OFF"
-    "-DCOMPILER_RT_BUILD_XRAY=OFF"
-    "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
-    "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ stdenv.lib.optionals (stdenv.hostPlatform.parsed.kernel.name == "none") [
-    "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
+  ] ++ stdenv.lib.optionals (bareMetal) [
     "-DCOMPILER_RT_OS_DIR=baremetal"
   ];
 
@@ -49,7 +57,7 @@ stdenv.mkDerivation rec {
   postPatch = stdenv.lib.optionalString stdenv.isDarwin ''
     substituteInPlace cmake/config-ix.cmake \
       --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
-  '' + stdenv.lib.optionalString (stdenv.hostPlatform.useLLVM or false) ''
+  '' + stdenv.lib.optionalString (useLLVM) ''
     substituteInPlace lib/builtins/int_util.c \
       --replace "#include <stdlib.h>" ""
     substituteInPlace lib/builtins/clear_cache.c \
@@ -61,7 +69,7 @@ stdenv.mkDerivation rec {
   # Hack around weird upsream RPATH bug
   postInstall = stdenv.lib.optionalString (stdenv.hostPlatform.isDarwin || stdenv.hostPlatform.isWasm) ''
     ln -s "$out/lib"/*/* "$out/lib"
-  '' + stdenv.lib.optionalString (stdenv.hostPlatform.useLLVM or false) ''
+  '' + stdenv.lib.optionalString (useLLVM) ''
     ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbegin.o
     ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/crtend.o
     ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
diff --git a/pkgs/development/compilers/llvm/9/default.nix b/pkgs/development/compilers/llvm/9/default.nix
index 11e44b8bdfa..d42e5187c3c 100644
--- a/pkgs/development/compilers/llvm/9/default.nix
+++ b/pkgs/development/compilers/llvm/9/default.nix
@@ -57,8 +57,10 @@ let
 
     libstdcxxClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
-      extraPackages = [
+      extraTools = [
         libstdcxxHook
+      ];
+      extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
       extraBuildCommands = mkExtraBuildCommands cc;
diff --git a/pkgs/development/compilers/rust/default.nix b/pkgs/development/compilers/rust/default.nix
index 1673441575c..d08b63dd643 100644
--- a/pkgs/development/compilers/rust/default.nix
+++ b/pkgs/development/compilers/rust/default.nix
@@ -18,8 +18,9 @@
       "armv7a" = "armv7";
       "armv7l" = "armv7";
       "armv6l" = "arm";
-    }.${cpu.name} or cpu.name;
-  in "${cpu_}-${vendor.name}-${kernel.name}${lib.optionalString (abi.name != "unknown") "-${abi.name}"}";
+    }.${cpu.name} or platform.rustc.arch or cpu.name;
+  in platform.rustc.config
+    or "${cpu_}-${vendor.name}-${kernel.name}${lib.optionalString (abi.name != "unknown") "-${abi.name}"}";
 
   makeRustPlatform = { rustc, cargo, ... }: rec {
     rust = {