gcc-wrapper: Get rid of builder.sh + cleanup
gcc-wrapper: Wrap ld.gold

This ensures that gcc's ‘-fuse-ld=gold’ flag works.
gcc-wrapper: Style fix
gcc-wrapper: Style fix
Unify gcc-wrapper and clang-wrapper
clang/llvm: Fewer build-time dependencies

Such as valgrind, dejagnu, tcl/tk, ...
libc++: Fix on Linux

On Linux (unlike Darwin), libc++ cannot automatically propagate
libc++abi. So we need to add libc++abi to the RPATH.
libc++abi: Drop dependency on libunwind

This appears no longer needed (libc++abi has its own libunwind). It
also prevents every libc++ user from depending on liblzma.