vlc: fix glx support

glx support is provided by the mesa3d package; so, enable it only when
mesa3d is part of the package selection.

Fixes:
  http://autobuild.buildroot.org/results/9b4/9b46021ea0064850ce8f1adcb5455d6da5bff459/build-end.log

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/vlc/vlc.mk

@@ -101,6 +101,13 @@ else
 VLC_CONF_OPT += --disable-flac
 endif
 
+ifeq ($(BR2_PACKAGE_MESA3D),y)
+VLC_CONF_OPT += --enable-glx
+VLC_DEPENDENCIES += mesa3d
+else
+VLC_CONF_OPT += --disable-glx
+endif
+
 ifeq ($(BR2_PACKAGE_OPUS),y)
 VLC_CONF_OPT += --enable-opus
 VLC_DEPENDENCIES += opus