Allow the element type of arrays to be incomplete in C++.
This fixes PR5048. Also fix a bug where zero-sized arrays weren't warned about when the size was unsigned.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@86136 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed