Disable the uninitialized field warning in uninstantiated classes.

If a templated class is not instantiated, then the AST for it could be missing
some things that would throw the field checker off.  Wait until specialization
before emitting these warnings.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220363 91177308-0d34-0410-b5e6-96231b3b80d8