[llvm] [AArch64] Have isel just do neg directly (PR #145185)

[David Green via llvm-commits]

davemgreen wrote:

Hi - Can you give some context on why you are interested in fast-isel? We don't use it by default at -O0 any more (it might still get used by some jits?). We don't tend to do a lot of extra work in fast-isel, and the work we add needs to balance the compile time impact against any runtime performance it would bring.

https://github.com/llvm/llvm-project/pull/145185