AST: Handle multidimensional arrays inside of __uuidof()

We previously handled one-dimensional arrays but didn't consider the
general case.  The fix is simple: keep going through subsequent
dimensions until we get to the base element.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191493 91177308-0d34-0410-b5e6-96231b3b80d8