Implement new C++ intrinsics __is_assignable and __is_constructible.

c-family/

Implement new C++ intrinsics __is_assignable and __is_constructible.
* c-common.c (__is_assignable, __is_constructible): New.
* c-common.h (RID_IS_ASSIGNABLE, RID_IS_CONSTRUCTIBLE): Likewise.

cp/

PR c++/80654
PR c++/80682
Implement new C++ intrinsics __is_assignable and __is_constructible.
* cp-tree.h (CPTK_IS_ASSIGNABLE, CPTK_IS_CONSTRUCTIBLE): New.
(is_xible): New.
* cxx-pretty-print.c (pp_cxx_trait_expression): Handle
CPTK_IS_ASSIGNABLE and CPTK_IS_CONSTRUCTIBLE.
* method.c (constructible_expr): Set cp_unevaluated.
(is_xible_helper): New.
(is_trivially_xible): Adjust.
(is_xible): New.
* parser.c (cp_parser_primary_expression): Handle
RID_IS_ASSIGNABLE and RID_IS_CONSTRUCTIBLE.
(cp_parser_trait_expr): Likewise.
* semantics.c (trait_expr_value): Handle
CPTK_IS_ASSIGNABLE and CPTK_IS_CONSTRUCTIBLE.

testsuite/

* g++.dg/ext/80654.C: New.

libstdc++-v3/

Implement new C++ intrinsics __is_assignable and __is_constructible.
* include/std/type_traits (__do_is_static_castable_impl): Remove.
(__is_static_castable_impl, __is_static_castable_safe): Likewise.
(__is_static_castable, __do_is_direct_constructible_impl): Likewise.
(__is_direct_constructible_impl): Likewise.
(__is_direct_constructible_new_safe): Likewise.
(__is_base_to_derived_ref, __is_lvalue_to_rvalue_ref): Likewise.
(__is_direct_constructible_ref_cast): Likewise.
(__is_direct_constructible_new, __is_direct_constructible): Likewise.
(__do_is_nary_constructible_impl): Likewise.
(__is_nary_constructible_impl, __is_nary_constructible): Likewise.
(__is_constructible_impl): Likewise.
(is_constructible): Call the intrinsic.
(__is_assignable_helper): Remove.
(is_assignable): Call the intrinsic.
(is_trivially_constructible): Likewise.
(__is_trivially_copy_constructible_impl): New.
(is_trivially_copy_constructible): Use it.
(__is_trivially_move_constructible_impl): New.
(is_trivially_move_constructible): Use it.
(is_trivially_assignable): Call the intrinsic.
(__is_trivially_copy_assignable_impl): New.
(is_trivially_copy_assignable): Use it.
(__is_trivially_move_assignable_impl): New.
(is_trivially_move_assignable): Use it.
(testsuite/20_util/declval/requirements/1_neg.cc): Adjust.
(testsuite/20_util/is_trivially_copy_assignable/value.cc):
Add test for void.
(testsuite/20_util/is_trivially_copy_constructible/value.cc): Likewise.
(testsuite/20_util/is_trivially_move_assignable/value.cc): Likewise.
(testsuite/20_util/is_trivially_move_constructible/value.cc): Likewise.
(testsuite/20_util/make_signed/requirements/typedefs_neg.cc): Adjust.
(testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc):
Likewise.

From-SVN: r248153