c++tools, configury: Configure with C++; test checking status [PR98821].

The c++tools configure fragments need to be built with a C++ compiler.

In addition, the stand-alone server uses diagnostic mechanisms in common
with GCC, but needs to define implementations for gcc_assert and
supporting output functions.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

PR c++/98821 - modules : c++tools configures with CC but code fragments assume CXX.

	PR c++/98821

c++tools/ChangeLog:

	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Configure using C++.  Pull logic to
	detect enabled checking modes; default to release
	checking.
	* server.cc (AI_NUMERICSERV): Define a fallback value.
	(gcc_assert): New.
	(gcc_unreachable): New.
	(fancy_abort): Only build when checking is enabled.

Co-authored-by: Jakub Jelinek <jakub@redhat.com>