[llvm] [FPEnv] Add strictfp attribute to the FP environment manipulation intrinsics (PR #96093)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> @arsenm, having the constrained intrinsics have strictfp specified in tablegen was your idea. Any thoughts?

[I think we should get rid of the constrained intrinsics](https://discourse.llvm.org/t/thought-on-strictfp-support/71453) altogether. This would mean we have intrinsic equivalents of all first class FP instructions, which would then have some kind of strictfp-like callsite attributes 

https://github.com/llvm/llvm-project/pull/96093