[llvm] [MCParser][NFCI] Deduplicate isIdentifierChar (PR #218100)

[via llvm-commits]

zhangweize9-cyber wrote:

> out-of-lining a hot function causes performance regression. i suspect you also make some places accept more characters

Sorry for the late reply. I tried several solutions locally, including the performance degradation of inline functions you mentioned. I first tried including the inline function in the `StringExtras` header file, but that didn't work. Then I tried `AsmLexer` and `AsmParser`, only to find that they had the same name. So, I could only try renaming one of the functions to `isStrictIdentifierChar` to solve this problem.

https://github.com/llvm/llvm-project/pull/218100