[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 noticed that there are some issue in compiler-rt implementation (e.g. CFLUSHOPT is not set). I plan to fix that (and other potential issue) in this PR and then merge

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