[clang] [llvm] [ARM] Emit an error when the hard-float ABI is enabled but can't be used. (PR #111334)

[Chris Copeland via cfe-commits]

chrisnc wrote:

I've updated this PR to remove the aforementioned `clang` warning for this case, and I've updated all `clang` and `llvm` tests that were implicitly using the soft-float ABI despite requesting hard-float. In some cases, explicitly testing hard-float seemed to be intended because there was a corresponding line for the soft-float version, so I added a feature or CPU selection that accomplishes this. In other cases, the hard-float-ness of the test did not seem relevant, so I just switched those to soft-float. I attempted to write a test case for the new LLVM error, but I'm struggling with having a `lit` test that tolerates `llc` exiting with a nonzero exit code, even if I can get the `CHECK` directives to match. Any pointers on this would be appreciated.

https://github.com/llvm/llvm-project/pull/111334