* include/experimental/numeric (gcd, lcm): Make bool arguments
	ill-formed.
	* include/std/numeric (gcd, lcm): Likewise.
	* testsuite/26_numerics/gcd/gcd_neg.cc: New test.
	* testsuite/26_numerics/lcm/lcm_neg.cc: New test.

From-SVN: r240919