Fix build on mingw32

My commit 897808e7 added a parameter to virCgroupGetPercpuStats,
but didn't change the stub for systems where cgroups are not supported.

src/util/vircgroup.c

@@ -4469,7 +4469,8 @@ virCgroupGetPercpuStats(virCgroupPtr group ATTRIBUTE_UNUSED,
                         virTypedParameterPtr params ATTRIBUTE_UNUSED,
                         unsigned int nparams ATTRIBUTE_UNUSED,
                         int start_cpu ATTRIBUTE_UNUSED,
-                        unsigned int ncpus ATTRIBUTE_UNUSED)
+                        unsigned int ncpus ATTRIBUTE_UNUSED,
+                        unsigned int nvcpupids ATTRIBUTE_UNUSED)
 {
     virReportSystemError(ENOSYS, "%s",
                          _("Control groups not supported on this platform"));