PowerPC's va_list, at least, is a typedef for an array, which means it
decays to a pointer in parameter position. Since the decayed type is
built from the array element type, the typedef sugar is lost.

More rdar://problem/25846421.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@286533 91177308-0d34-0410-b5e6-96231b3b80d8