configure script never translates "powerpc64" to "ppc64" ... it
just assumes it will get back "ppc64" ...

--- configure
+++ configure
@@ -1384,6 +1384,9 @@
 	powerpc )
 		host_cpu="ppc"
 		;;
+	powerpc64 )
+		host_cpu="ppc64"
+		;;
 	* )
 		host_cpu="$host_cpu"
 		;;