test if xen is enabled only once

Signed-off-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

configure

@@ -1690,6 +1690,7 @@ if test "$bluez" = "yes" ; then
   echo "#define CONFIG_BLUEZ 1" >> $config_host_h
 fi
 if test "$xen" = "yes" ; then
+  echo "CONFIG_XEN=y" >> $config_host_mak
   echo "XEN_LIBS=$xen_libs" >> $config_host_mak
 fi
 if test "$aio" = "yes" ; then
@@ -1766,10 +1767,6 @@ else
     exit 1
 fi
 
-if test "$xen" = "yes" ; then
-  echo "CONFIG_XEN=y" >> $config_host_mak
-fi
-
 tools=
 if test `expr "$target_list" : ".*softmmu.*"` != 0 ; then
   tools="qemu-img\$(EXESUF) $tools"