include declarations for new stdio_ext functions (gnulib support)

include/stdio_ext.h

@@ -20,6 +20,11 @@ size_t __fbufsize(FILE *);
 size_t __fpending(FILE *);
 int __fpurge(FILE *);
 
+size_t __freadahead(FILE *);
+const char *__freadptr(FILE *, size_t *);
+void __freadptrinc(FILE *, size_t);
+void __fseterr(FILE *);
+
 #ifdef __cplusplus
 }
 #endif