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

[Khem Raj via llvm-commits]

kraj wrote:

> Assuming that that ATPCS, APCS and AAPCS are referring to the ABI names [1]. The APCS and ATPCS are pre ABI (2004 ish). I think ARM Linux stayed on the pre-ABI PCS for some time after that, but I don't think that would be supported anymore in GCC.

I waa trying to add musl support and `musleabi` ,  speaking from Yocto's use of it, use of `-mabi=` has been long gone. 

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