[llvm] [GlobalISel][AArch64] Legalize G_FABS and G_FNEG for SVE (PR #114784)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

There are no SVE patterns for fneg today. Either there is no demand for them or C++ is more efficient.

For GlobalISel, we have 
* fneg pattern with implicit_def
* fneg pattern with movprfx
* C++

fneg is just an example. There are many predicated (merging and/or zeroing) instructions without  good pattern coverage.

https://github.com/llvm/llvm-project/pull/114784