In my most recent pull from SVN, alsa.m4 freetype2.m4 xaw.m4 xorg-macros.m4 xorg-server.m4 xorgversion.m4 xtrans.m4 are showing up in .../build_i686/staging_dir/usr/share/aclocal and I believe that a recent change requires them to be in .../build_i686/host_dir/usr/share/aclocal. I'm not quite sure how to get them to build there, but if I copy them by hand my build completes otherwise it crashes trying to build xorg.
Actually it's the other way around. r25827 wrongly changed the aclocal search dir to point to HOST_DIR instead of STAGING_DIR. It's fixed in r25880.