[llvm] [InstCombine] Ensure Safe Handling of Flags in foldFNegIntoConstant (PR #94148)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> If we directly use `FNegOp`, it breaks some `reassoc` tests.

Do you have an example? Those tests might just be wrong

https://github.com/llvm/llvm-project/pull/94148