Include <cstdlib> for abs()

AMDmi3 · Endless Sky · commit 392227f164ae · 2017-08-31T10:57:44.000-04:00
diff --git a/source/CollisionSet.cpp b/source/CollisionSet.cpp
@@ -20,6 +20,7 @@ PARTICULAR PURPOSE.  See the GNU General Public License for more details.
 #include "Ship.h"
 
 #include <algorithm>
+#include <cstdlib>
 #include <numeric>
 #include <set>
 
