[clang-tools-extra] [clang-tidy] Fix false negatives in performance-faster-string-find with libstdc++ (PR #185559)

[via cfe-commits]

zeyi2 wrote:

> btw, I think the repro can be reduced to just this (https://godbolt.org/z/G86E3hK68):
> 
> ```c++
> template <typename T> struct Wrapper {
>   T value;
> };
> 
> void f() {
>     Wrapper<std::string>().value.find("a");
> }
> ```

Thanks!

(I'm still trying to understand what's going on with Windows CI, seems like there is another encoding problem o_o)

https://github.com/llvm/llvm-project/pull/185559