fixup! sys/string_utils: add string_writer helper

sys/include/string_utils.h

@@ -30,6 +30,7 @@
 #include <strings.h>
 #include <sys/types.h>
 
+#include "flash_utils.h"
 #include "modules.h"
 
 #ifndef STRING_UTILS_H
@@ -98,7 +99,8 @@ static inline const char *string_writer_str(const string_writer_t *sw)
  * @return      number of bytes written on success
  *              -E2BIG if the string was truncated
  */
-int swprintf(string_writer_t *sw, const char *restrict format, ...);
+__attribute__ ((format (printf, 2, 3)))
+int swprintf(string_writer_t *sw, FLASH_ATTR const char *restrict format, ...);
 
 /* explicit_bzero is provided if:
  * - glibc is used as C lib (only with board natvie)