When we can't prove that the target of an aggregate copy is

When we can't prove that the target of an aggregate copy is
a complete object, the memcpy needs to use the data size of
the structure instead of its sizeof() value.  Fixes PR12204.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@153613 91177308-0d34-0410-b5e6-96231b3b80d8