[clang] Add clang warning if fp exception functions are called without appropriate flags/pragmas (#128239) (PR #187860)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

This is looking good; just some minor issues before we can merge:

Please update the PR description (the first comment in the PR) to describe the updated implementation.

Please don't put the issue number in the title; put a separate "Fixes #128239" line in the description.

Please add a release note (clang/docs/ReleaseNotes.rst).

https://github.com/llvm/llvm-project/pull/187860