[COMMITTED] Improve coment for the newly added code in ipa-split.

It was pointed out to me by Jakub, that the comment in front of
the new code which handles warning/error attribute was not really
understandable. This fixes the comment to be understandable; I
don't know why I wrote the original comment that way even.

Committed as obvious after a quick build.

gcc/ChangeLog:

	* ipa-split.cc (visit_bb): Fix comment before the
	warning/error attribute checking code.