[clang] [llvm] [Clang][Lexer] Reland "Detect SSE4.2 availability at runtime in fastParseASCIIIdentifier" (PR #180631)

[Thibault Monnier via cfe-commits]

Thibault-Monnier wrote:

They are not available with gcc on Windows (or Solaris), and broke some Chromium configurations. You can find the reports in the previous PR, after it was merged.

https://github.com/llvm/llvm-project/pull/180631