silence C23 warning

buffer/buffer_stubborn.c

@@ -1,7 +1,7 @@
 #include <errno.h>
 #include "buffer.h"
 
-ssize_t buffer_stubborn(ssize_t (*op)(),int fd,const char* buf, size_t len,void* cookie) {
+ssize_t buffer_stubborn(ssize_t (*op)(int fd,const char* buf,size_t len,void* cookie),int fd,const char* buf, size_t len,void* cookie) {
   ssize_t w;
   errno=0;
   while (len) {

buffer/buffer_stubborn2.c

@@ -1,7 +1,7 @@
 #include <errno.h>
 #include "buffer.h"
 
-ssize_t buffer_stubborn_read(ssize_t (*op)(),int fd,const char* buf, size_t len,void* cookie) {
+ssize_t buffer_stubborn_read(ssize_t (*op)(int fd,const char* buf,size_t len,void* cookie),int fd,const char* buf, size_t len,void* cookie) {
   ssize_t w;
   for (;;) {
     if ((w=op(fd,buf,len,cookie))<0)