[clang] [llvm] [CodeGen][LLVM] Make the `va_list` related intrinsics generic. (PR #85460)

[Alexander Richardson via cfe-commits]

https://github.com/arichardson approved this pull request.

LGTM thanks! Please wait for @jrtc27 to also approve before committing though.

https://github.com/llvm/llvm-project/pull/85460