[v3 PATCH] Implement LWG 2733 and LWG 2759

[Jonathan Wakely]

On 14/11/17 18:14 +0200, Ville Voutilainen wrote:
>    Implement LWG 2733 and LWG 2759
>    * include/experimental/numeric (gcd): Reject cv-qualified bool.
>    (lcm): Likewise.
>    * include/std/numeric (gcd): Likewise.
>    (lcm): Likewise.
>    * testsuite/26_numerics/gcd/gcd_neg.cc: Add tests and adjust.
>    * testsuite/26_numerics/lcm/lcm_neg.cc: Likewise.

Both files can use remove_cv_t instead of remove_cv::type (and there's
no need to std-qualify it in std::gcd).

They could also use is_integral_v and is_same_v but that's
pre-existing, and less important because there's no 'typename' that
can be avoided by changing it.