Fixed compilation of ClipperUtils on GCC, which is more strict than VS2013 compiler.
Fixed compilation of ClipperUtils on GCC, which is more strict
than VS2013 compiler.

prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r,prusa3d/Slic3r