The struct timeval is defined in sys/time.h

--- eloop.h	2014-07-14 22:56:47.000000000 +0200
+++ eloop.h	2015-10-11 09:49:29.563643314 +0200
@@ -29,6 +29,7 @@
 #define ELOOP_H
 
 #include <time.h>
+#include <sys/time.h>
 
 int add_event(int, void (*)(void *), void *);
 int add_event_flags(int, short, void (*)(int, void *), void *);
