The current gambit fails to compile with GCC-7.2.0

Upstream fix: gambitproject/gambit@b911156 (see also issue 220)

Tarball: https://downloads.sourceforge.net/project/gambit/gambit15/15.1.1/gambit-15.1.1.tar.gz?r=https%3A%2F%2Fsourceforge.net%2Fprojects%2Fgambit%2Ffiles%2Fgambit15%2F15.1.1&ts=1507718641&use_mirror=kent

Upstream: Fixed upstream, but not in a stable release.

Component: packages: optional

Author: Jeroen Demeyer

Branch/Commit: 6fc099e

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/24012