[llvm] [AArch64] Fall back to SelectionDAG ISel if GISel is not feasible. (PR #196343)

[Sander de Smalen via llvm-commits]

sdesmalen-arm wrote:

> Though I do wonder if fallBackToDAGISel should also be controlling when GISel is enabled (it looks like we now enable GISel when it's disabled, then fallback for cases where it shouldn't be enabled https://github.com/llvm/llvm-project/pull/174746/changes#r2812855555, IIUC).

Thanks for the suggestion, I'll see if I can put up an NFCI follow-up for this.

https://github.com/llvm/llvm-project/pull/196343