- include strings.h

Thanks to Rich Felker for pointing this out.

editors/awk.c

@@ -12,6 +12,7 @@
 #include <unistd.h>
 #include <errno.h>
 #include <string.h>
+#include <strings.h>
 #include <time.h>
 #include <math.h>
 #include <ctype.h>