while building xserver:

make[3]: Entering directory `/sources/X.org/xserver/hw/dmx/input'
if 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/X/include -I/usr/include/freetype2   -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  -DHAVE_DMX_CONFIG_H  -I/usr/X/include -I/usr/include/freetype2   -g -O2 -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':

File xf86Keymap.h is provided by driver/xf86-input-keyboard:

package xorg:/sources/X.org> find driver/ |grep xf86Keymap.h 
driver/xf86-input-keyboard/src/xf86Keymap.h

But if I'm trying to build it first it will give me:

/sources/X.org/driver/xf86-input-keyboard> ./autogen.sh --prefix=/usr/X
....
checking dependency style of gcc... (cached) gcc3
./configure: line 19567: syntax error near unexpected token `RANDR,'
./configure: line 19567: `XORG_DRIVER_CHECK_EXT(RANDR, randrproto)'

Function XORG_DRIVER_CHECK_EXT is defined in xserver/xorg-server.m4

So, to install xserver one will need driver/xf86-input-keyboard to be installed, to install driver/xf86-input-keyboard one will need to install xserver first.