Fix a problem Eli ran into where we now reject incomplete arrays of

Fix a problem Eli ran into where we now reject incomplete arrays of
uncompleted struct types.  We now do what llvm-gcc does and compile
them into [i8 x 0].  If the type is later completed, we make sure that
it is appropriately cast.

We compile the terrible example to something like this now:

%struct.A = type { i32, i32, i32 }

@g = external global [0 x i8]

define void @_Z1fv() nounwind {
entry:
  call void @_Z3fooP1A(%struct.A* bitcast ([0 x i8]* @g to %struct.A*))
  ret void
}

declare void @_Z3fooP1A(%struct.A*)

define %struct.A* @_Z2f2v() nounwind {
entry:
  ret %struct.A* getelementptr inbounds ([0 x %struct.A]* bitcast ([0 x i8]* @g to [0 x %struct.A]*), i32 0, i64 1)
}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@134972 91177308-0d34-0410-b5e6-96231b3b80d8