[llvm] [InstSimplify] Defer to ConstantFold in simplifyInstrinsic (PR #205061)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

This patch is incorrect because strictfp != ebStrict, and is broken: will update once if we validate and land https://github.com/llvm/llvm-project/pull/209465.

https://github.com/llvm/llvm-project/pull/205061