clang: Pass -platform-version to new MachO LLD

New MachO LLD doesn't implement the old -macos_version_min (etc)
flags, but it understands the modern platform_version flag.
So make the clang driver pass that when using new MachO LLD.

Also, while here, don't pass -lto_library to LLD, since it
links in LTO libraries statically (which it can because it's
versioned alongside clang).

Differential Revision: https://reviews.llvm.org/D92037