xosd: require and link against Xlib.

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>
(cherry picked from commit 3254502d)

configure.ac

@@ -3848,8 +3848,13 @@ if test "${enable_xosd}" = "yes"
 then
   AC_CHECK_HEADERS(xosd.h,
     AC_CHECK_LIB(xosd, xosd_set_horizontal_offset, [
-      VLC_ADD_PLUGIN([xosd])
-      VLC_ADD_LIBS([xosd],[-lxosd])
+      AS_IF([test "${no_x}" != "yes"], [
+          VLC_ADD_PLUGIN([xosd])
+          VLC_ADD_LIBS([xosd],[-lxosd ${X_LIBS} ${X_PRE_LIBS} -lX11])
+          VLC_ADD_CFLAGS([xosd],[${X_CFLAGS}])
+        ],[
+          AC_MSG_ERROR([Xlib is required with xosd.])
+        ])
     ])
   )
 fi