player.c: Add missing header

As required by rand(3).

src/player/src/human_player_gui.c

@@ -56,7 +56,7 @@ static void on_add_walker(void *const arg)
     it->show = false;
 }
 
-static void on_exit(void *const arg)
+static void on_btn_exit(void *const arg)
 {
     struct human_player *const h = arg;
 
@@ -117,7 +117,7 @@ static void update_items(struct human_player *const h)
         b->u.type1.w = 80;
         b->common.hcentered = true;
         b->u.type1.label.text = "Exit";
-        b->on_pressed = on_exit;
+        b->on_pressed = on_btn_exit;
         b->arg = h;
         gui_add_child(&it->topcnt.common, &b->common);
     }

src/player/src/player.c

@@ -3,6 +3,7 @@
 #include <unit.h>
 #include <terrain.h>
 #include <stddef.h>
+#include <stdlib.h>
 
 void player_update(struct player *const p)
 {

src/terrain/src/init.c

@@ -1,6 +1,7 @@
 #include <terrain.h>
 #include <ctype.h>
 #include <errno.h>
+#include <inttypes.h>
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>