[clang] [clang][CodeGen] Ensure consistent `mustprogress` attribute emission across all paths (PR #71452)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

The C equivalent to the C++11 rule is in 6.8.5, which says "An iteration statement may be assumed by the implementation to terminate if [...]".  There's no general rule that a program has to make progress if there isn't a loop involved.

https://github.com/llvm/llvm-project/pull/71452