lib: Make libvirt ACPI feature flag conditional on x86 or Arm

On ppc64 and s390x it failed with an error like:

  unsupported configuration: machine type 'pseries-10.0' does not support ACPI

Updates: commit 7cf0ed750e
Related: https://bugzilla.redhat.com/show_bug.cgi?id=2372329

lib/launch-libvirt.c

@@ -1175,9 +1175,12 @@ construct_libvirt_xml_cpu (guestfs_h *g,
 
   single_element_format ("vcpu", "%d", g->smp);
 
+#if defined(__i386__) || defined(__x86_64__) || \
+  defined(__arm__) || defined(__aarch64__)
   start_element ("features") {
     empty_element ("acpi");
   } end_element ();
+#endif
 
   start_element ("clock") {
     attribute ("offset", "utc");