cmake: fix build WITH_SOUND=OFF

Signed-off-by: Alexander Golubev <fatzer2@gmail.com>

src/kernel/CMakeLists.txt

@@ -48,7 +48,6 @@ set( _SRC_ qtaddons_x11.cpp
            qpaintdevice_x11.cpp
            qpainter_x11.cpp
            qregion_x11.cpp
-           qsound_x11.cpp
            qwidget_x11.cpp
            qwidgetcreate_x11.cpp
            qfontengine_x11.cpp
@@ -109,7 +108,6 @@ set( _SRC_ qtaddons_x11.cpp
            qsizegrip.cpp
            qstyle.cpp
            qsocketnotifier.cpp
-           qsound.cpp
            qstylesheet.cpp
            qthread.cpp
            qtimer.cpp
@@ -133,6 +131,11 @@ set( _SRC_ qtaddons_x11.cpp
            qpngio.cpp
            qaccessible.cpp
 )
+
+if( WITH_SOUND )
+    list( APPEND _SRC_ qsound.cpp qsound_x11.cpp )
+endif()
+
 if( WITH_GLIBMAINLOOP )
     list( APPEND _SRC_ qeventloop_x11_glib.cpp qeventloop_unix_glib.cpp )
  else()