Tweak Sema::ObjCQualifiedIdTypesAreCompatible() to handle qualified interface types on the RHS.

This eliminates a bogus warning identified in the test below.

This fixes <rdar://problem/5968256> clang on xcode: error: incompatible type initializing 'NSObject<XCSelectionSource> *', expected 'id<NSObject,XCSelectionSource>'

llvm-svn: 51832