Fix a gross typo: ARMv6+ may or may not support unaligned memory operations.

Fix a gross typo: ARMv6+ may or may not support unaligned memory operations.
Even if they are suported by the core, they can be disabled
(this is just a configuration bit inside some register).

Allow unaligned memops on darwin and conservatively disallow them otherwise.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94889 91177308-0d34-0410-b5e6-96231b3b80d8