[FPEnv][X86] Correct strictfp tests. (#87791)

Correct strictfp tests to follow the rules documented in the LangRef:
https://llvm.org/docs/LangRef.html#constrained-floating-point-intrinsics

These tests needed the strictfp attribute added to some function
definitions. FP wait instructions now appear as a result.

Test changes verified with D146845.