We're using %r13 like on NetBSD instead of %r11.

--- callback/vacall_r/vacall-rs6000-linux.s.orig	Mon Jan 29 13:55:18 2001
+++ callback/vacall_r/vacall-rs6000-linux.s	Sun Apr 26 07:01:24 2009
@@ -35,8 +35,8 @@ __vacall_r:
 	stw 9,20(1)
 	addi 0,1,48
 	stw 0,40(1)
-	lwz 9,0(11)
-	lwz 3,4(11)
+	lwz 9,0(13)
+	lwz 3,4(13)
 	addi 4,1,8
 	mtlr 9
 	blrl