[PATCH] Fix for nasty LTO issue that's most obvious in ObjectiveC.

[David Majnemer]

>>! In D6145#11, @freik wrote:
> @rnk: I considered both, and am new to the codebase, so the 'correct' place to fix this wasn't apparent. Does anyone else have an opinion, here? Either way is effective, and pretty straightforward as well.

I think the idea is that `copyAttributesFrom` is intended to handle all attributes which are defaulted when a `GlobalObject` is created.

Now that I am reviewing `GlobalObject::copyAttributesFrom`, it looks like we forgot to handle `Comdat` there as well.

http://reviews.llvm.org/D6145