[clang] [llvm] [Clang][Lexer] Reland "Detect SSE4.2 availability at runtime in fastParseASCIIIdentifier" (PR #175452)

[Thibault Monnier via cfe-commits]

Thibault-Monnier wrote:

Thanks. I think I'll require using Linux or MacOS instead to avoid a long blacklist.

https://github.com/llvm/llvm-project/pull/175452