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

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Missing semantic analysis.  Since the signature is unspecified in Builtin.td, you have to check that there's one argument, and that argument is an integer.  That code should go in SemaChecking.cpp.

You can leave constant evaluation to a followup, sure.

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