Add missing #includes.

Change-Id: I81405d638f80fc96874ea0b21af3538229aa38a7
diff --git a/libcorkscrew/map_info.c b/libcorkscrew/map_info.c
index f33378f..3c52854 100644
--- a/libcorkscrew/map_info.c
+++ b/libcorkscrew/map_info.c
@@ -21,6 +21,7 @@
 
 #include <ctype.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <limits.h>
 #include <pthread.h>