[llvm] ARM: Read float ABI from the "float-abi" module flag (PR #212981)

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

I'm still a bit confused by the comment in the test about the module flag for none.ll and no instance of `-float-abi` , would be nice if that can be clarified, but otherwise LGTM and no objections to merging. 

https://github.com/llvm/llvm-project/pull/212981