c++: Implement __is_volatile built-in trait
This patch implements built-in trait for std::is_volatile.
gcc/cp/ChangeLog:
* cp-trait.def: Define __is_volatile.
* constraint.cc (diagnose_trait_expr): Handle CPTK_IS_VOLATILE.
* semantics.cc (trait_expr_value): Likewise.
(finish_trait_expr): Likewise.
gcc/testsuite/ChangeLog:
* g++.dg/ext/has-builtin-1.C: Test existence of __is_volatile.
* g++.dg/ext/is_volatile.C: New test.
Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
Reviewed-by: Jason Merrill <jason@redhat.com>