Diamond tiling helper function cone complement hyperplane doesn't have a GLPK path

[bondhugula]

When diamond tiling is enabled, the ILP used by find_cone_complement_hyperplane doesn't have a path through GLPK - it always uses either ISL or PIP irrespective of whether --glpk is specified. Moreover, there isn't even a method pluto_constraints_lexmin_glpk (consistent with the isl/pip-based methods for lexmin) although there is a pluto_prog_constraints_lexmin_glpk and pluto_fcg_constraints_solve_glpk.

Not using GLPK in some cases can lead to high solver time or overflows with ISL or PIP.

Test case reported by: Hengjie on pluto-development@googlegroups.com.