Declare and define implicit move constructor and assignment operator.

Declare and define implicit move constructor and assignment operator.

This makes the code duplication of implicit special member handling even worse,
but the cleanup will have to come later. For now, this works.
Follow-up with tests for explicit defaulting and enabling the __has_feature
flag to come.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@138821 91177308-0d34-0410-b5e6-96231b3b80d8