bsd_signal's prototype unavailable when _GNU_SOURCE is defined

[Florian Weimer]

* Ponnuvel Palaniyappan:

> Is this the expected behaviour? If so, is there a way to make bsd_signal
> available whiling _GNU_SOURCE is defined?

It's not listed in NEWS, so it's not deliberate.  But considering that
the function is obsolete, I would say the bug is that it's not
mentioned in NEWS, not that the declaration has been removed from the
header file.