[llvm] ARM: Remove check for isAAPCS_ABI when enabling various aeabi calls (PR #152108)

[Matt Arsenault via llvm-commits]

arsenm wrote:

I don't have any particular interest in keeping or removing -mabi; my issue is this is just untested complexity in the backend. If there was test coverage there wouldn't be an issue 

https://github.com/llvm/llvm-project/pull/152108