strchrnul: include header

src/include/strchrnul.c

@@ -23,6 +23,8 @@
 #include <string.h>
 #include <stdlib.h>
 
+#include "strchrnul.h"
+
 /* Find the first occurrence of C in S or the final NUL byte.  */
 char *strchrnul(const char *s, int c_in)
 {