[clang] [Clang] [Lexer] Detect SSE4.2 availability at runtime in fastParseASCIIIdentifier (PR #171914)

[Thibault Monnier via cfe-commits]

Thibault-Monnier wrote:

Thanks for reporting this. I'm currently in the process of reverting this change at #174946 until I can inspect the issues.

https://github.com/llvm/llvm-project/pull/171914