[clang] [libcxx] [Clang] Add __builtin_invoke and use it in libc++ (PR #116709)

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https://github.com/cor3ntin commented:

Thanks for working on that. Do you have any benchmarks?

- Please add an entry in LanguageExensions.rst
-  Can you add a minimum of tests for static  / explicit object member functions, lambdas?
- Something like https://compiler-explorer.com/z/s5s9sbzn7

I think my general concern here is "did we forget something? 

https://github.com/llvm/llvm-project/pull/116709