[llvm] [AArch64][SVE] Rework VECTOR_COMPRESS lowering (PR #171162)

[Gaëtan Bossu via llvm-commits]

https://github.com/gbossu commented:

Drive-by comments. This looks sane to me, but I need to get more familiar with the legalisation code for `compress`.

https://github.com/llvm/llvm-project/pull/171162