bpo-39648: Expand math.gcd() and math.lcm() to handle multiple arguments. (GH-18604)

* bpo-39648: Expand math.gcd() and math.lcm() to handle multiple arguments.

* Simplify fast path.

* Difine lcm() without arguments returning 1.

* Apply suggestions from code review

Co-Authored-By: Mark Dickinson <dickinsm@gmail.com>

Co-authored-by: Mark Dickinson <dickinsm@gmail.com>