IRgen/NeXT: Fix several alignment issues with Objective-C metadata symbols:

IRgen/NeXT: Fix several alignment issues with Objective-C metadata symbols:
 - Fix some places that had the alignment hard coded.
 - Use ABI type alignment, not preferred type alignment -- neither of this is exactly right, as we really want the C type alignment as required by the runtime, but the ABI alignment is a more correct choice.

This should be equivalent for x86_64, but fixes the alignment for ARM.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@102314 91177308-0d34-0410-b5e6-96231b3b80d8