Fix makefile targets. Remove unnecessary warnings.

src/ai.c

@@ -1,3 +1,4 @@
+#include <stdlib.h>
 #include "ai.h"
 #include "engine.h"
 #include "gfx.h"
@@ -6,6 +7,7 @@ const char moves[] = {'w', 'a', 's', 'd'};
 
 int ai_move(struct gamestate *g)
 {
+    /* Ensure srand is called somewhere prior */
     if (g->opts->interactive) gfx_sleep(50);
     return moves[rand() % 4];
 }