package/x11r7/xserver_xorg-server: fix gcc5+ build with version 1.14.7

package/x11r7/xserver_xorg-server: fix gcc5+ build with version 1.14.7

Fixes

sdksyms.c:311:15: error: expected expression before »,« token
     (void *) &,                                                  /* ../../include/os.h:96 */

by backporting an upstream patch, sdksyms.c is generated by
hw/xfree86/sdksyms.sh which is broken when used with gcc5+.

Problem was found while testing
http://patchwork.ozlabs.org/patch/762102/

using this defconfig

BR2_TOOLCHAIN_BUILDROOT_WCHAR=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
BR2_PACKAGE_XORG7=y
BR2_PACKAGE_XSERVER_XORG_SERVER=y
BR2_PACKAGE_XSERVER_XORG_SERVER_V_1_14=y
BR2_PACKAGE_XDRIVER_XF86_INPUT_TSLIB=y

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>