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

[via cfe-commits]

Andarwinux wrote:

The original PR had the following description:

> If the binary is compiled with SSE4.2 enabled, or if we are not compiling for x86, then the behavior is the exact same, ensuring we have no regressions.

But this is no longer in the description of this PR, does this mean that the new PR no longer supports the use of -msse4.2 to eliminate runtime detection?



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