crunchgen: add prototype to skeleton code

Currently this warning scrolls by when building ramdisks:

------------------->
instbin.c:64:15: warning: passing arguments to a function without a prototype is deprecated in all versions of C and is not supported in C23
[-Wdeprecated-non-prototype]
   64 |                 return ep->f(argc, argv, envp);
      |                             ^
1 warning generated.
<-------------------

Add the missing prototype to the crunchgen skeleton code.
OK?

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commit 19abba37379d47a931d6143a59525d46df76ba96 (local)
from: Christian Weisgerber <[email protected]>
date: Fri Aug  7 15:26:11 2026 UTC
 
 one more prototype
 
diff 4eab5a0e1a710925a784ad1664915671c957a294 19abba37379d47a931d6143a59525d46df76ba96
commit - 4eab5a0e1a710925a784ad1664915671c957a294
commit + 19abba37379d47a931d6143a59525d46df76ba96
blob - 3b56e2d042d1ceac305e477a56bb14d70c8dcbda
blob + 07a0228887206fde6136b6439f839f84e27bf187
--- usr.sbin/crunchgen/crunched_main.c
+++ usr.sbin/crunchgen/crunched_main.c
@@ -39,7 +39,7 @@
 
 struct stub {
 	char	*name;
-	int	(*f)();
+	int	(*f)(int, char **, char **);
 };
 
 extern struct stub entry_points[];

-- 
Christian "naddy" Weisgerber                          [email protected]