ARM: test default values for TAG_CPU_unaligned_access attribute.

It should be on for every target that supports unaligned accesses (e.g. not
v6m).

Patch by Charlie Turner.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220912 91177308-0d34-0410-b5e6-96231b3b80d8