[llvm] [AArch64] Fix build-bot assertion error in AArch64 (PR #154124)

[via llvm-commits]

AZero13 wrote:

The root cause is that in global isel I forgot to include the logic that treats -1 as a legal immediate.

This will have to be included and approved in a separate PR. For now, just bail as we did before the change that caused this assertion.

Also doing it too in SelDag just to be safe.

https://github.com/llvm/llvm-project/pull/154124