[llvm] [AArch64][GlobalISel] Skip RegBankSelect pass at -O0 (PR #199040)

[Amara Emerson via llvm-commits]

aemerson wrote:

> I think the correct replacement is to have a trivial regbankselect replacement pass rather than deferring the assignment to the selector, and introducing a new edge case where regbanks aren't set coming into selection. The trivial pass could amount to memset 

Agreed. This was a known cost that we paid willingly for the sake of our overall design.

https://github.com/llvm/llvm-project/pull/199040