Running 

PATH=/usr/X11R7.2/bin:$PATH build.sh -m path_to_mesa /usr/X11R7.2

after git_xorg dies at:

-I../../../xfixes -I../../../Xi -I../../../mi -I../../../miext/shadow 
-I../../../miext/damage -I../../../render -I../../../randr -I../../../fb
-I../../../hw/dmx -I../../../hw/xfree86/common -I/home/ronis/xc/mesa//include
-DHAVE_DMX_CONFIG_H -I/usr/X11R7.2/include   -I/usr/X11R7.2/include   -O3
-march=pentium4 -ffast-math -funroll-loops -fomit-frame-pointer -MT
ChkNotMaskEv.o -MD -MP -MF ".deps/ChkNotMaskEv.Tpo" -c -o ChkNotMaskEv.o
ChkNotMaskEv.c; \
	then mv -f ".deps/ChkNotMaskEv.Tpo" ".deps/ChkNotMaskEv.Po"; else rm -f
".deps/ChkNotMaskEv.Tpo"; exit 1; fi
if /usr/bin/gcc -DHAVE_CONFIG_H -I. -I. -I../../../include -I../../../include
-I../../../include -I../../../include -I../../../include -I../../../include
-I../../../include -I../../../include    -DHAVE_DIX_CONFIG_H -Wall
-Wpointer-arith -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations
-Wnested-externs -fno-strict-aliasing -D_BSD_SOURCE -DHAS_FCHOWN
-DHAS_STICKY_DIR_BIT -I/usr/X11R7.2/include -I/usr/include/dbus-1.0
-I/usr/lib/dbus-1.0/include   -I../../../include -I../../../include
-I../../../Xext -I../../../composite -I../../../damageext -I../../../xfixes
-I../../../Xi -I../../../mi -I../../../miext/shadow  -I../../../miext/damage
-I../../../render -I../../../randr -I../../../fb -I../../../hw/dmx
-I../../../hw/xfree86/common -I/home/ronis/xc/mesa//include -DHAVE_DMX_CONFIG_H
-I/usr/X11R7.2/include   -I/usr/X11R7.2/include   -O3 -march=pentium4
-ffast-math -funroll-loops -fomit-frame-pointer -MT lnx-keyboard.o -MD -MP -MF
".deps/lnx-keyboard.Tpo" -c -o lnx-keyboard.o lnx-keyboard.c; \
	then mv -f ".deps/lnx-keyboard.Tpo" ".deps/lnx-keyboard.Po"; else rm -f
".deps/lnx-keyboard.Tpo"; exit 1; fi
lnx-keyboard.c:167:24: error: xf86Keymap.h: No such file or directory
lnx-keyboard.c: In function 'kbdLinuxReadKernelMapping':
lnx-keyboard.c:803: error: 'map' undeclared (first use in this function)
lnx-keyboard.c:803: error: (Each undeclared identifier is reported only once
lnx-keyboard.c:803: error: for each function it appears in.)
lnx-keyboard.c: In function 'kbdLinuxGetMap':
lnx-keyboard.c:930: error: 'map' undeclared (first use in this function)
make[3]: *** [lnx-keyboard.o] Error 1

Sure enough there is no xf86Keymap.h in this directory, although there is one in 
driver/xf86-input-keyboard/src

I commented on this problem in Bug #8892 but haven't heard anything.