Fix a GCCism.

int foo[0];  // dodgy
int foo[];   // means the same, works the same and survives lint.

Tested by:	3 months of use on my laptop

sys/sys/proc.h

@@ -114,7 +114,7 @@ struct procsig {
 struct pargs {
 	u_int	ar_ref;		/* Reference count. */
 	u_int	ar_length;	/* Length. */
-	u_char	ar_args[0];	/* Arguments. */
+	u_char	ar_args[];	/* Arguments. */
 };
 
 /*-