This is LWG issue 3349.

	* include/std/complex (__cpp_lib_constexpr_complex): Define.
	* include/std/version (__cpp_lib_constexpr_complex): Likewise.
	* testsuite/26_numerics/complex/1.cc: New test.
	* testsuite/26_numerics/complex/2.cc: New test.

From-SVN: r279172