[llvm] [AArch64][GlobalISel] Constrain G_CONSTANT_FOLD_BARRIER operand register classes (PR #177997)

[David Green via llvm-commits]

https://github.com/davemgreen approved this pull request.

Thanks - this sounds OK to me but please wait to see if @arsenm thinks it should work differently.

https://github.com/llvm/llvm-project/pull/177997