Don't propagate StorageClass and ComplexType to aliases.

This matches gas' behaviour on COFF.

I think that this yak is now sufficiently shaved for aliases with offset
to work.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207786 91177308-0d34-0410-b5e6-96231b3b80d8