[clang] [llvm] [AArch64] Add soft-float ABI (PR #74460)

[Ties Stuij via cfe-commits]

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

This seems like a sensible and unobtrusive solution to me. Also the change is backed by a change in the Arm ABI, and it looks like the other review comments have been addressed. I've also built this change locally and ran the lit tests, and everything passes.

https://github.com/llvm/llvm-project/pull/74460