Propagate alignment for _Complex

_Complex load/store didn't have their alignment set properly, which was visible when GCC's torture tests use volatile _Complex.

Update some existing tests to check for alignment, and add a new test which also has over-aligned volatile _Complex (since the imaginary part shouldn't be overaligned, only the real part).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186490 91177308-0d34-0410-b5e6-96231b3b80d8