[clang] [clang] Provide an SSE4.2 implementation of identifier token lexer (PR #68962)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> @serge-sans-paille I'm still trying to understand whether this change will be tested by CI - or at all. SSE4 is not enabled by default and i don't think our cmake does that either - I did ping @AaronBallman and we are still thinking about it

I think we're in good shape for testing because we have at least one bot that's set up to compile for cascade lake, which does support SSE 4.2: https://github.com/llvm/llvm-zorg/blob/4bc450165fa9fcef26adca5a80f4d97b9d6babc3/buildbot/osuosl/master/config/builders.py#L827 so I believe that gets us the test coverage we need. Any disagreement?

https://github.com/llvm/llvm-project/pull/68962