make -k distclean
git clean -dfx

LDFLAGS="-L/home/andy/Src/Xorg-git/modular/lib" ./autogen.sh --prefix=/home/andy/Src/Xorg-git/modular --disable-egl --enable-texture-float --enable-gallium-g3dvl --enable-r600-llvm-compiler --with-gallium-drivers=r600,swrast --with-dri-drivers= 

Also tried adding CPPFLAGS="-I/home/andy/Src/Xorg-git/modular/include"

PKG_CONFIG_PATH and ACLOCAL are set up to above path where xorg, mesa and libdrm are installed.

since - 

commit 998d975e38db7478781130b42a4fb68d6b181055
Author: Daniel Martin <consume.noise@gmail.com>
Date:   Thu Feb 28 19:39:06 2013 +0100

    Fix build of swrast only without libdrm

In file included from dri_screen.c:33:0:
../../../../../src/mesa/drivers/dri/common/xmlpool.h:96:29: fatal error: xmlpool/options.h: No such file or directory
compilation terminated.
make[5]: *** [dri_screen.lo] Error 1
make[5]: *** Waiting for unfinished jobs....
make[5]: Leaving directory `/mnt/sdb1/Src/Mesa-git/mesa/src/gallium/state_trackers/dri/drm'
make[4]: *** [all-recursive] Error 1
make[4]: Leaving directory `/mnt/sdb1/Src/Mesa-git/mesa/src/gallium/state_trackers/dri'
make[3]: *** [all-recursive] Error 1
make[3]: Leaving directory `/mnt/sdb1/Src/Mesa-git/mesa/src/gallium/state_trackers'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/mnt/sdb1/Src/Mesa-git/mesa/src/gallium'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/mnt/sdb1/Src/Mesa-git/mesa/src'
make: *** [all-recursive] Error 1