AArch64/ARM64: implement diagnosis of unpredictable loads & stores

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208091 91177308-0d34-0410-b5e6-96231b3b80d8
Be more strict about not calling setAlignment on global aliases.

The fact that GlobalAlias::setAlignment exists at all is a side effect of
how the classes are organized, it should never be used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208094 91177308-0d34-0410-b5e6-96231b3b80d8