c++: Improve access checking inside templates [PR41437]

c++: Improve access checking inside templates [PR41437]

This patch generalizes our existing functionality for deferring access
checking of typedefs when parsing a function or class template to now
defer all kinds of access checks until template instantiation time,
including member function and member object accesses.

Since all access checks eventually go through enforce_access, the main
component of this patch is new handling inside enforce_access to defer
the current access check if we're inside a template.  The bulk of the
rest of the patch consists of removing now-unneeded code pertaining to
suppressing access checks inside templates or pertaining to
typedef-specific access handling.  Renamings and other changes with no
functional impact have been split off into the followup patch.

gcc/cp/ChangeLog:

	PR c++/41437
	PR c++/47346
	* call.c (enforce_access): Move to semantics.c.
	* cp-tree.h (enforce_access): Delete.
	(get_types_needing_access_check): Delete.
	(add_typedef_to_current_template_for_access_check): Delete.
	* decl.c (make_typename_type): Adjust accordingly.  Use
	check_accessibility_of_qualified_id instead of directly using
	perform_or_defer_access_check.
	* parser.c (cp_parser_template_declaration_after_parameters):
	Don't push a dk_no_check access state when parsing a template.
	* pt.c (get_types_needing_access_check): Delete.
	(append_type_to_template_for_access_check_1): Delete.
	(perform_typedefs_access_check): Adjust.  If type_decl is a
	FIELD_DECL, also check its DECL_CONTEXT for dependence. Use
	tsubst_copy instead of tsubst to substitute into type_decl so
	that we substitute into the DECL_CONTEXT of a FIELD_DECL.
	(append_type_to_template_for_access_check): Delete.
	* search.c (accessible_p): Remove the processing_template_decl
	early exit.
	* semantics.c (enforce_access): Moved from call.c.  If we're
	parsing a template and the access check failed, add the check to
	TI_TYPEDEFS_NEEDING_ACCESS_CHECKING.
	(perform_or_defer_access_check): Adjust comment.
	(add_typedef_to_current_template_for_access_check): Delete.
	(check_accessibility_of_qualified_id):  Adjust accordingly.
	Exit early if the scope is dependent.

gcc/testsuite/ChangeLog:

	PR c++/41437
	PR c++/47346
	* g++.dg/cpp2a/concepts-using2.C: Adjust.
	* g++.dg/lto/20081219_1.C: Adjust.
	* g++.dg/lto/20091002-1_0.C: Adjust.
	* g++.dg/lto/pr65475c_0.C: Adjust.
	* g++.dg/opt/dump1.C: Adjust.
	* g++.dg/other/pr53574.C: Adjust.
	* g++.dg/template/access30.C: New test.
	* g++.dg/template/access31.C: New test.
	* g++.dg/wrappers/wrapper-around-type-pack-expansion.C: Adjust.

libstdc++-v3/ChangeLog:

	PR libstdc++/94003
	* testsuite/20_util/is_constructible/94003.cc: New test.