Add linux-headers to QEMU_INCLUDES

virtio/dataplane/vring.c requires the Linux headers and is built for all
targets. So we need to add the corresponding include to QEMU_INCLUDES to
avoid that outdated distribution headers are used.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

configure

@@ -544,6 +544,7 @@ Haiku)
   if [ "$cpu" = "i386" -o "$cpu" = "x86_64" ] ; then
     audio_possible_drivers="$audio_possible_drivers fmod"
   fi
+  QEMU_INCLUDES="-I\$(SRC_PATH)/linux-headers $QEMU_INCLUDES"
 ;;
 esac
 
@@ -4227,10 +4228,6 @@ else
 fi
 includes="-I\$(SRC_PATH)/tcg $includes"
 
-if test "$linux" = "yes" ; then
-  includes="-I\$(SRC_PATH)/linux-headers $includes"
-fi
-
 for i in $ARCH $TARGET_BASE_ARCH ; do
   case "$i" in
   alpha)