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

[Mikołaj Piróg via cfe-commits]

mikolaj-pirog wrote:

This change brings some ABI stability, by explicitly assigning bits to ABI_VALUE. Still the situation is not ideal because we need to make updates in compiler-rt and X86TargerParser.def. I think that a natural solution is to have compiler-rt include X86TargetParser.def and use its tables -- would that be an acceptable from compiler-rt perspective? @compnerd

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