Fix getIntegerTypeOrder() to properly handle enums by first unwrapping their underlying integer type.  This is a precondition for calling getIntegerRank().

Fixes an assertion failure in a test case involving vectors.

Fixes <rdar://problem/15091442>

Please somebody check this.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192334 91177308-0d34-0410-b5e6-96231b3b80d8