c.opt (Wmultiple-inheritance, [...]): New C++ warnings.

c.opt (Wmultiple-inheritance, [...]): New C++ warnings.

	c-family/
	* c.opt (Wmultiple-inheritance, Wvirtual-inheritance, Wtemplates,
	Wnamespaces): New C++ warnings.

	cp/
	* decl.c (xref_basetypes): Check virtual and/or multiple
	inheritance warning.
	* parser.c (cp_parser_namespace_definition): Check namespaces
	warning.
	* pt.c (push_template_decl_real): Check templates warning.

	* doc/invoke.texi  (-Wmultiple-inheritance, -Wvirtual-inheritance,
	-Wtemplates, -Wnamespaces): Document.

	testsuite/
	* g++.dg/diagostic/disable.C: New.

From-SVN: r228019