[clang] [CIR] Add MemChrOp for __builtin_char_memchr and __builtin_memchr (PR #175234)

[Sirui Mu via cfe-commits]

https://github.com/Lancern requested changes to this pull request.

Could you add a test for `__builtin_memchr` as well?

https://github.com/llvm/llvm-project/pull/175234