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

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

Thanks, this seems to work for me for mingw with GCC. But please replace the PR description, which will be the commit message once merged, with something more like the original one - and I'd appreciate if you'd omit the usernames from the commit message - see https://discourse.llvm.org/t/forbidding-username-in-commits/86997.

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