Merge staging-next into staging

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";