Improve -Wuninitialized warnings for fields that are record types.

Get the record handling code from SelfReferenceChecker into
UninitializedFieldVisitor as well as copying the testcases.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@218740 91177308-0d34-0410-b5e6-96231b3b80d8