... and mitigate PR c++/42336

gcc/cp/ChangeLog:
	PR c++/42758
	PR c++/42634
	PR c++/42336
	PR c++/42797
	PR c++/42880
	* cp-tree.h (NON_DEFAULT_TEMPLATE_ARGS_COUNT,
	SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT,
	GET_NON_DEFAULT_TEMPLATE_ARGS_COUNT): New accessor macros.
	* pt.c (coerce_template_parms, type_unification_real,
	expand_template_argument_pack, coerce_template_parameter_pack):
	Set the non default template args count.
	(current_template_args): Always set non defaulted
	template args count when compiled with --enable-checking
	(tsubst_template_args, type_unification_real): Propagate the non
	defaulted template args count.
	* error.c (get_non_default_template_args_count): Renamed
	count_non_default_template_args into this. Don't calculate the
	non default template argument count anymore. Use the new
	accessor macros above to get it.
	(dump_template_argument_list, dump_type, dump_decl,
	dump_template_parms): Adjust.
	* parser.c (cp_parser_template_argument_list): Always set defaulted
	template args count when compiled with --enable-checking.

gcc/testsuite/ChangeLog:
	PR c++/42758
	PR c++/42634
	PR c++/42336
	PR c++/42797
	PR c++/42880
	* g++.dg/other/crash-5.C: New test.
	* g++.dg/other/crash-6.C: New test.
	* g++.dg/other/crash-7.C: New test.
	* g++.dg/other/crash-8.C: New test.

From-SVN: r156351