Simplify the base characteristics for some type traits

Simplify the base characteristics for some type traits

	* include/std/type_traits (__is_member_object_pointer_helper): Use
	__not_<is_function<_Tp>>::type instead of integral_constant.
	(__is_member_function_pointer_helper): Likewise for
	is_function<_Tp>::type.
	(is_compund): Likewise for __not_<is_fundamental<_Tp>>::type.
	(__do_is_nt_destructible_impl): Use __bool_constant and reindent.
	(is_trivially_constructible): Remove redundant use of
	is_constructible.
	(__is_trivially_copy_assignable_impl): Remove redundant use of
	is_copy_assignable.
	(__is_trivially_move_assignable_impl): Remove redundant use of
	is_move_assignable.
	(is_trivially_destructible): Use __bool_constant.
	* testsuite/20_util/is_trivially_assignable/value.cc: Add some more
	tests for scalar types.

From-SVN: r262889