Need to include limits.h for the definition of PATH_MAX.

--- src/core/cpufreq.cc	2015-10-14 10:07:06.646338278 +0200
+++ src/core/cpufreq.cc	2015-10-14 10:08:09.092333406 +0200
@@ -10,6 +10,7 @@
 #include "version.h"
 #include "hw.h"
 #include "osutils.h"
+#include <limits.h>
 #include <string.h>
 #include <sys/types.h>
 #include <sys/stat.h>
