compat: stub out _rs_forkhandler for compat/arc4random.c

We need to keep the fd open at fork, but we retained the code to
handle a fork.

The original update to chacha avoided this by guarding the call
but left the code alive which produced an unused function warning
on the GitHub Ubuntu runner.
This update fixes that.

compat/arc4random.c

@@ -78,7 +78,14 @@ static int _dhcpcd_rand_fd = -1;	/* /dev/urandom fd */
 
 static int _dhcpcd_getentropy(void *, size_t);
 static inline int _rs_allocate(struct _rs **, struct _rsx **);
+
+/* dhcpcd needs to hold onto the fd at fork due to privsep */
+#if 0
 static inline void _rs_forkdetect(void);
+#else
+#define _rs_forkdetect()
+#define _rs_forkhandler()
+#endif
 
 /* Inline "arc4random.h" */
 #include <sys/types.h>
@@ -89,7 +96,6 @@ static inline void _rs_rekey(u_char *dat, size_t datlen);
 /* dhcpcd isn't multithreaded */
 #define _ARC4_LOCK()
 #define _ARC4_UNLOCK()
-#define _ARC4_ATFORK(f)
 
 static int
 _dhcpcd_getentropy(void *buf, size_t length)
@@ -126,6 +132,7 @@ _getentropy_fail(void)
 	raise(SIGKILL);
 }
 
+#if 0
 static volatile sig_atomic_t _rs_forked;
 
 static inline void
@@ -148,6 +155,7 @@ _rs_forkdetect(void)
 			memset(rs, 0, sizeof(*rs));
 	}
 }
+#endif
 
 static inline int
 _rs_allocate(struct _rs **rsp, struct _rsx **rsxp)
@@ -163,7 +171,7 @@ _rs_allocate(struct _rs **rsp, struct _rsx **rsxp)
 		return (-1);
 	}
 
-	_ARC4_ATFORK(_rs_forkhandler);
+	_rs_forkhandler();
 	return (0);
 }