in favour of teaching CCAssignToStack that size 0 and/or align
0 means to use the ABI values. This seems a neater solution.
It is safe since no legal value type has size 0.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44107 91177308-0d34-0410-b5e6-96231b3b80d8