Use syscall::exit instead of the nonexistent syscall::rexit.

MFC after:	1 week

cddl/contrib/opensolaris/cmd/dtrace/test/tst/common/pid/tst.vfork.d

@@ -54,7 +54,7 @@ pid$1:a.out:go:
 	exit(1);
 }
 
-syscall::rexit:entry
+syscall::exit:entry
 /pid == $1/
 {
 	exit(0);