Right now, at least in CVS head (I haven't checked releases), amd64 never has
the cpuid code called. Trivial patch to get it called:

cvs diff: Diffing liboil
Index: liboil/liboilcpu.c
===================================================================
RCS file: /cvs/liboil/liboil/liboil/liboilcpu.c,v
retrieving revision 1.32
diff -u -r1.32 liboilcpu.c
--- liboil/liboilcpu.c  19 May 2006 06:56:08 -0000      1.32
+++ liboil/liboilcpu.c  15 Jun 2006 12:07:52 -0000
@@ -743,7 +743,7 @@
 static void
 oil_cpu_detect_arch(void)
 {
-#ifdef __i386__
+#if defined(__i386__) || defined(__amd64__)
   oil_cpu_detect_i386();
 #endif
 #if defined(__powerpc__) || defined(__PPC__) || defined(__ppc__)