procutils: include missing header

To be able to use DIR we need to include the dirent.h header. This fixes issues such as:

../include/procutils.h:5: error: syntax error before "DIR"
../include/procutils.h:5: warning: no semicolon at end of struct or union

Signed-off-by: Davidlohr Bueso <dave@gnu.org>

include/procutils.h

@@ -1,6 +1,8 @@
 #ifndef UTIL_LINUX_PROCUTILS
 #define UTIL_LINUX_PROCUTILS
 
+#include <dirent.h>
+
 struct proc_tasks {
 	DIR *dir;
 };