type_traits (declval): Add, per DR 1255.

type_traits (declval): Add, per DR 1255.

2009-11-12  Paolo Carlini  <paolo.carlini@oracle.com>

	* include/std/type_traits (declval): Add, per DR 1255.
	(__is_convertible_helper, common_type): Use it.
	* include/bits/move.h: Mention std::declval.
	* testsuite/20_util/declval/requirements/1.cc: New.
	* testsuite/20_util/declval/requirements/1_neg.cc: Likewise.
	* testsuite/20_util/common_type/requirements/typedefs-2.cc: Likewise.
	* testsuite/20_util/common_type/requirements/
	explicit_instantiation.cc: Extend.
	* testsuite/20_util/make_signed/requirements/typedefs_neg.cc: Adjust
	dg-error line numbers.
	* testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc:
	Likewise.

From-SVN: r154140