Fix all implicit declarations

AC_HEADER_TIME is only needed if you need to include time.h and
sys/time.h at the same time.

The truth is this codebase is an unholy mess but at least this fixes
the warnings.

icc.c

@@ -5,6 +5,7 @@
 #include "style.h"
 #include "prefs.h"
 
+#include <stdlib.h>
 #include <string.h>
 #include <stdlib.h>