treewide: Start to break up static overlay

We can use use `stdenv.hostPlatform.isStatic` instead, and move the
logic per package. The least opionated benefit of this is that it makes
it much easier to replace packages with modified ones, as there is no
longer any issue of overlay order.

CC @FRidh @matthewbauer

pkgs/development/compilers/llvm/10/libc++/default.nix

@@ -1,5 +1,6 @@
 { lib, stdenv, fetch, cmake, python3, libcxxabi, fixDarwinDylibNames, version
-, enableShared ? true }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++";

pkgs/development/compilers/llvm/10/libc++abi.nix

@@ -1,5 +1,6 @@
 { stdenv, cmake, fetch, libcxx, libunwind, llvm, version
-, enableShared ? true }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++abi";

pkgs/development/compilers/llvm/10/libunwind.nix

@@ -1,4 +1,6 @@
-{ stdenv, version, fetch, cmake, fetchpatch, enableShared ? true }:
+{ stdenv, version, fetch, cmake, fetchpatch
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation rec {
   pname = "libunwind";

pkgs/development/compilers/llvm/11/libc++/default.nix

@@ -1,5 +1,6 @@
 { lib, stdenv, fetch, cmake, python3, libcxxabi, llvm, fixDarwinDylibNames, version
-, enableShared ? true }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++";

pkgs/development/compilers/llvm/11/libc++abi.nix

@@ -1,5 +1,6 @@
 { stdenv, cmake, fetch, libcxx, libunwind, llvm, version
-, enableShared ? true }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++abi";

pkgs/development/compilers/llvm/11/libunwind.nix

@@ -1,4 +1,6 @@
-{ stdenv, version, fetch, cmake, fetchpatch, enableShared ? true }:
+{ stdenv, version, fetch, cmake, fetchpatch
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation rec {
   pname = "libunwind";

pkgs/development/compilers/llvm/7/libc++/default.nix

@@ -1,5 +1,6 @@
 { lib, stdenv, fetch, cmake, python3, libcxxabi, fixDarwinDylibNames, version
-, enableShared ? ! stdenv.hostPlatform.isMusl }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++";

pkgs/development/compilers/llvm/7/libc++abi.nix

@@ -1,7 +1,8 @@
 { stdenv, cmake, fetch, libcxx, llvm, version
 , standalone ? false
   # on musl the shared objects don't build
-, enableShared ? ! stdenv.hostPlatform.isMusl }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++abi";

pkgs/development/compilers/llvm/8/libc++/default.nix

@@ -1,5 +1,6 @@
 { lib, stdenv, fetch, cmake, python3, libcxxabi, fixDarwinDylibNames, version
-, enableShared ? true }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++";

pkgs/development/compilers/llvm/8/libc++abi.nix

@@ -1,5 +1,6 @@
 { stdenv, cmake, fetch, libcxx, libunwind, llvm, version
-, enableShared ? true }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++abi";

pkgs/development/compilers/llvm/8/libunwind.nix

@@ -1,4 +1,6 @@
-{ stdenv, version, fetch, cmake, fetchpatch, enableShared ? true }:
+{ stdenv, version, fetch, cmake, fetchpatch
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libunwind";

pkgs/development/compilers/llvm/9/libc++/default.nix

@@ -1,5 +1,6 @@
 { lib, stdenv, fetch, cmake, python3, libcxxabi, fixDarwinDylibNames, version
-, enableShared ? true }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++";

pkgs/development/compilers/llvm/9/libc++abi.nix

@@ -1,5 +1,6 @@
 { stdenv, cmake, fetch, libcxx, libunwind, llvm, version
-, enableShared ? true }:
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation {
   pname = "libc++abi";

pkgs/development/compilers/llvm/9/libunwind.nix

@@ -1,4 +1,6 @@
-{ stdenv, version, fetch, cmake, fetchpatch, enableShared ? true }:
+{ stdenv, version, fetch, cmake, fetchpatch
+, enableShared ? !stdenv.hostPlatform.isStatic
+}:
 
 stdenv.mkDerivation rec {
   pname = "libunwind";