kbuild_helper.h: Add required #include (#2000)

kbuild_helper.h: Add required #include ftw.h

src/cc/frontends/clang/kbuild_helper.cc

@@ -15,7 +15,6 @@
  */
 #include <fcntl.h>
 #include <stdlib.h>
-#include <ftw.h>
 #include <iostream>
 #include "kbuild_helper.h"
 

src/cc/frontends/clang/kbuild_helper.h

@@ -19,6 +19,7 @@
 #include <vector>
 #include <unistd.h>
 #include <errno.h>
+#include <ftw.h>
 
 namespace ebpf {