Flag synthesized struct decl. as non-empty so
CXX side of ir gen does not skip its Null initialization.
Fixes radar 8027844 for objc++'s collection statement.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@104837 91177308-0d34-0410-b5e6-96231b3b80d8