Objective-C IRGen. Patch to generate a weak symbol reference when
'super' dispatches a class method in category for OBJC_METACLASS.
This is when class is a weak_import class.
// rdar://16529125


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210547 91177308-0d34-0410-b5e6-96231b3b80d8