ObjectiveC migrator: In suggesting 'instancetype' use clang's
hasRelatedResultType() as it knows of methods which have
related result type by default. Such methods do not need
a redundant 'instancetype'.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189520 91177308-0d34-0410-b5e6-96231b3b80d8