sync with latest bpf-next (#10)

sync with latest bpf-next. tested with fb internal testcase and bcc.

Signed-off-by: Yonghong Song <yhs@fb.com>

src/libbpf.c

@@ -18,6 +18,7 @@
 #include <libgen.h>
 #include <inttypes.h>
 #include <string.h>
+#include <strings.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>