[llvm] [FPEnv][PowerPC] Correct one more strictfp test. (PR #94793)

[Qiu Chaofan via llvm-commits]

ecnelises wrote:

`setflm` `readflm` reads and writes FPSCR (the register containing fp exception bits) so it should have strictfp attr. Is there anything needed to add in clang? Currently I marked the two builtins as `IntrNoMerge, IntrHasSideEffects`.

By the way, does the constrained intrinsics not need strictfp attr?

https://github.com/llvm/llvm-project/pull/94793