[clang] [Sema] Implement fix as suggested by FIXME (PR #143142)

[Nikita Popov via cfe-commits]

nikic wrote:

Looks neutral: https://llvm-compile-time-tracker.com/compare.php?from=e4060d3beab3b525b49baaa15484e3c595740a2f&to=aace43c7cc60347e1853e55ee7c033a19a9a65ea&stat=instructions:u

max-rss seems to have an improvement on tramp3d-v4 in multiple configurations, so that's probably not noise: https://llvm-compile-time-tracker.com/compare.php?from=e4060d3beab3b525b49baaa15484e3c595740a2f&to=aace43c7cc60347e1853e55ee7c033a19a9a65ea&stat=max-rss

https://github.com/llvm/llvm-project/pull/143142