[llvm] [AArch64] -aarch64-enable-global-isel-at-O=-1 should disable GISel (PR #182250)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Why is -1 an accepted value at all? I'd expect this to be a hard error 

https://github.com/llvm/llvm-project/pull/182250