[Patch][BZ 14583] Fix prototype of sigsetjmp in pthread.h

[Roland McGrath]

> Shall I update setjmp/setjmp.h with appropriate line-wrapping as well?

Sure, feel free.  I think it's in the "obvious" category.  That's the kind
of thing that we don't usually try to be especially pro-active about when
violations have snuck in at some time in the past.  We just don't let new
errors go in with new changes.  But it never hurts to fix the old ones.