With --disable-GL why xserver compiles in GL subdir?

[Yotam Medini]

Using modular util/modular/build.sh
and setting the CONFFLAGS environment variable with 
export CONFFLAGS="--disable-GL --disable-glx --disable-aiglx --disable-glx-tls --disable-dri --disable-xgl"
I could see that these options find their way to some
sub packages configure scripts.

But I wonder why xserver/xorg bother to compile in
xserver/xorg/GL/glx at all.  
It fails there on me since I did not bother to provide Mesa-source
directory.

-- yotam