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

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Please fix your GitHub settings so your email address is public.  Looks like the bot didn't trigger for some reason; see https://github.com/llvm/llvm-project/pull/82429#issuecomment-1955214651 for the normal message.

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