ARM-MachO: stop claiming to be EABI

Embedded ARM MachO targets are AAPCS but not full EABI (we don't use
__aeabi_whatever and the functions are allowed to be hard-float).

Turns out there was already a test for this, but its original purpose had
become corrupted over the years.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@269487 91177308-0d34-0410-b5e6-96231b3b80d8