package/x11r7/xlib_libxshmfence: needs sync_4

package/x11r7/xlib_libxshmfence: needs sync_4

Also propagate reverse dependency to mesa3d and xserver_xorg-server.

Fixes xserver_xorg-server build
http://autobuild.buildroot.net/results/7da/7da8b46cda8786422e8293f26b79582b35a433d6/

For patch discussion refer to http://patchwork.ozlabs.org/patch/674595/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
[Thomas: only select BR2_PACKAGE_XPROTO_PRESENTPROTO if
BR2_TOOLCHAIN_HAS_SYNC_4 is available, add comment explaining why.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>