[clang] [clang] Implement __builtin_popcountg (PR #82359)

[Nick Desaulniers via cfe-commits]

nickdesaulniers wrote:

> @nickdesaulniers I am interested in implementing more builtins like this one. :)


Cool, I've filed:
1. https://github.com/llvm/llvm-project/issues/83075
2. https://github.com/llvm/llvm-project/issues/83076

Those would be helpful to have next, and I suspect as straight foward to implement as popcountg was.

https://github.com/llvm/llvm-project/pull/82359