treewide: NIX_*_COMPILE -> string

pkgs/development/compilers/openjdk/8.nix

@@ -140,7 +140,7 @@ let
 
     separateDebugInfo = true;
 
-    NIX_CFLAGS_COMPILE = [
+    NIX_CFLAGS_COMPILE = toString ([
       # glibc 2.24 deprecated readdir_r so we need this
       # See https://www.mail-archive.com/openembedded-devel@lists.openembedded.org/msg49006.html
       "-Wno-error=deprecated-declarations"
@@ -151,13 +151,13 @@ let
       "-fno-delete-null-pointer-checks"
       "-std=gnu++98"
       "-Wno-error"
-    ];
+    ]);
 
-    NIX_LDFLAGS= lib.optionals (!headless) [
+    NIX_LDFLAGS= toString (lib.optionals (!headless) [
       "-lfontconfig" "-lcups" "-lXinerama" "-lXrandr" "-lmagic"
     ] ++ lib.optionals (!headless && enableGnome2) [
       "-lgtk-x11-2.0" "-lgio-2.0" "-lgnomevfs-2" "-lgconf-2"
-    ];
+    ]);
 
     buildFlags = [ "all" ];
 

pkgs/development/compilers/rust/rustc.nix

@@ -41,11 +41,11 @@ in stdenv.mkDerivation rec {
   # See: https://github.com/NixOS/nixpkgs/pull/56540#issuecomment-471624656
   stripDebugList = [ "bin" ];
 
-  NIX_LDFLAGS =
+  NIX_LDFLAGS = toString (
        # when linking stage1 libstd: cc: undefined reference to `__cxa_begin_catch'
        optional (stdenv.isLinux && !withBundledLLVM) "--push-state --as-needed -lstdc++ --pop-state"
     ++ optional (stdenv.isDarwin && !withBundledLLVM) "-lc++"
-    ++ optional stdenv.isDarwin "-rpath ${llvmSharedForHost}/lib";
+    ++ optional stdenv.isDarwin "-rpath ${llvmSharedForHost}/lib");
 
   # Increase codegen units to introduce parallelism within the compiler.
   RUSTFLAGS = "-Ccodegen-units=10";