libstdc++: Document remaining C++17 implementation-defined behavior.

This also covers bad_function_call::what from C++11.

libstdc++-v3/ChangeLog:

	* doc/html/manual/status.html: Regenerate.
	* doc/xml/manual/status_cxx2011.xml: Add entry for bad_function_call.
	* doc/xml/manual/status_cxx2017.xml: Add entries for bad_any_cast
	and nullptr_t output. Update entry for sf.cmath. Fix stable name for
	mem.res.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
(cherry picked from commit 39d7c4d42a764a86644198a517f58a94f467cdbd)