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

[Rainer Orth via cfe-commits]

rorth wrote:

This patch badly broke the [Solaris/amd64 buildbot](https://lab.llvm.org/staging/#/builders/120/builds/15410), introducing 390 testsuite failures.  All of them follow the same pattern, which can be seen on `libclang.so.23.0.0git` directly:
```
$ ldd -r ld.so.1: libclang.so.23.0.0git: fatal: relocation error: R_AMD64_PC32: file lib/libclang.so.23.0.0git: symbol __cpu_model: value 0xa9123062 does not fit
```

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