Removing a C++11'ism to also fix the build bots.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201517 91177308-0d34-0410-b5e6-96231b3b80d8
The default assignment operator could not be generated by all of the bots, but it's required by std::vector to operate properly.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@201518 91177308-0d34-0410-b5e6-96231b3b80d8