vircgroup: Fix broken builds without cgroups

I missed adding virCgroupNewIOThread to the !VIR_CGROUP_SUPPORTED

Pushing as build breaker

src/util/vircgroup.c

@@ -3982,6 +3982,18 @@ virCgroupNewEmulator(virCgroupPtr domain ATTRIBUTE_UNUSED,
 }
 
 
+int
+virCgroupNewIOThread(virCgroupPtr domain ATTRIBUTE_UNUSED,
+                     int iothreadid ATTRIBUTE_UNUSED,
+                     bool create ATTRIBUTE_UNUSED,
+                     virCgroupPtr *group ATTRIBUTE_UNUSED)
+{
+    virReportSystemError(ENXIO, "%s",
+                         _("Control groups not supported on this platform"));
+    return -1;
+}
+
+
 int
 virCgroupNewDetect(pid_t pid ATTRIBUTE_UNUSED,
                    int controllers ATTRIBUTE_UNUSED,