Refactored error reporting in CheckObjCDealloc and CheckObjCInstMethSignature to use this new bug reporting interface (major code simplification).

llvm-svn: 53560

llvm-svn: 53493

ObjCImplementationDecls and sees if a ancestor class defines a method with the
same selector but with a different type signature. Right now it just compares
return types, and mainly looks at differences in primitive values. The checking
will be expanded in the future.

llvm-svn: 53482