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

[Thorsten Schütt via llvm-commits]

tschuett wrote:

A miscompile is caused by ordering issues:
https://github.com/llvm/llvm-project/issues/78383
Nonetheless, I would expect UNDEF and catching misbeviour be executed/registered before optimizations.

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