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

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I'm a little surprised we don't need any LLVM backend changes, but I guess in soft-float mode we basically treat floats as ints anyway, so maybe things just work.  I'd like to see appropriate regression tests, though (if they don't already exist).

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