[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:

clang-format picked up issues in the latest version.

I'd like to see a bit more test coverage for the new code related to fexcept_t: in particular, that we generate the correct error if the definition is missing, that we generate correct diagnostics for a function declaration that doesn't match, and verifying that AST serialization works.  You might be able to extend existing tests for this; there should be tests for all of this for the existing builtins.

Please add a clang regression test for the potentially-evaluated thing, so we don't need to depend on libcxx tests to check it.

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