[llvm] [GlobalISel] replace right identity X * -1.0 with fneg(x) (PR #80526)

[Nick Anderson via llvm-commits]

nickleus27 wrote:

> This is OK, we are allowed to drop canonicalizes for non-strictfp functions. The DAG is too strict and I've been meaning to remove those restrictions

Does this mean the matcher should be checking for FMafn flags or check that the function has UnsafeFPMath?

https://github.com/llvm/llvm-project/pull/80526