[clang] [compiler-rt] [llvm] [X86] Sync multiversion features with libgcc and refactor internal feature tables (PR #168750)

[Mikołaj Piróg via llvm-commits]

mikolaj-pirog wrote:

I've pushed a last small change -- I've enabled multiversioning on x86-64, since that's what compiler-rt and libgcc expect (x86-64 being different than x86-64-v1).

I will be fixing bugs in latter PRs, I don't want to include more changes here

https://github.com/llvm/llvm-project/pull/168750