xserver-xorg: rewrite xorg-server.m4 patch

xserver-xorg: rewrite xorg-server.m4 patch

Instead of having a patch that upstream won't accept, rewrite it in a
upstreamable way and <gasp> submit it upstream.

The fundamental problem is that pkg-config --variable=sdkdir will return the
value of sdkdir literally, whereas --cflags will return -I${sdkdir} *but* will
do sysroot relocation magic on the path so it is usable.

Signed-off-by: Ross Burton <ross.burton@intel.com>