[clang] [flang] [llvm] Add clang warning if fp exception functions are called without appropriate flags/pragmas (PR #199009)

[Eli Friedman via llvm-commits]

================
@@ -20,6 +21,7 @@ using namespace Fortran::parser::literals;
 
 void HostFloatingPointEnvironment::SetUpHostFloatingPointEnvironment(
     FoldingContext &context) {
+  FLANG_FENV_ACCESS_ON
----------------
efriedma-quic wrote:

This isn't sufficient to get the right semantics.

The way SetUpHostFloatingPointEnvironment() is implemented, it is itself a function that isn't legal to call without appropriate flags/pragmas.  So the caller (ApplyHostFunctionHelper) also needs FLANG_FENV_ACCESS_ON.

Same applies to other places.  (Including, I think, the change from https://github.com/llvm/llvm-project/pull/200268.)

https://github.com/llvm/llvm-project/pull/199009