The element passed to push_back is not copied before the vector reallocates.
The client needs to copy the element first before passing it to push_back.
No test case, will be tested by follow-up swift scheduler model change (it
segfaults without this change).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183459 91177308-0d34-0410-b5e6-96231b3b80d8