Referenced implementation from Fuchsia and Darwin Toolchain.
Still only support CST_Libcxx. Now checks that the argument
is really '-stdlib=libc++', and display error.
Also, now will pass -lc++ and -lc++abi to the linker.
Patch by Patrick Cheng!
Differential Revision: https://reviews.llvm.org/D41937
llvm-svn: 322382