c++: Add -Wexceptions warning option [PR97675]

This PR asks that we add a warning option for an existing (very old)
warning, so that it can be disabled selectively.  clang++ uses
-Wexceptions for this, so I added this new option rather than using
e.g. -Wnoexcept.

gcc/c-family/ChangeLog:

	PR c++/97675
	* c.opt (Wexceptions): New option.

gcc/cp/ChangeLog:

	PR c++/97675
	* except.c (check_handlers_1): Use OPT_Wexceptions for the
	warning.  Use inform for the second part of the warning.

gcc/ChangeLog:

	PR c++/97675
	* doc/invoke.texi: Document -Wexceptions.

gcc/testsuite/ChangeLog:

	PR c++/97675
	* g++.old-deja/g++.eh/catch10.C: Adjust dg-warning.
	* g++.dg/warn/Wexceptions1.C: New test.
	* g++.dg/warn/Wexceptions2.C: New test.