[llvm] [llvm][AArch64] Preserve regmask when expanding the BLR_BTI pseudo instruction (PR #73927)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

Thanks for the quick fix! I'm not familiar with this area of the code so I can't comment on the implementation of the fix, but I can confirm that it does fix my original issue!

https://github.com/llvm/llvm-project/pull/73927