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

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Please also update `clang/docs/LanguageExtensions.rst` to document the new builtin, and update `clang/docs/ReleaseNotes.rst` so users know about the new functionality.

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