While making the X server:

then mv -f ".deps/utils.Tpo" ".deps/utils.Plo"; else rm -f ".deps/utils.Tpo"; exit 1; fi
 gcc -DHAVE_CONFIG_H -I. -I. -I../include -I../include -I../include -I../include -I../include -I../include -
I../include -I../include -I../include -no-cpp-precomp -I/usr/include/openssl -I/sw/include/pango-1.0 
-I/sw/lib/freetype219/include -I/sw/lib/freetype219/include/freetype2 -I/sw/lib/fontconfig2/include -
I/sw/include/libpng12 -I/usr/local/include -I/sw/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/include -I/sw/lib/
freetype219/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 -pipe -fPIC -O0 
-mcpu=7450 -mtune=7450 -MT utils.lo -MD -MP -MF .deps/utils.Tpo -c utils.c  -fno-common -DPIC 
-o .libs/utils.o
In file included from /usr/include/signal.h:63,
                 from /usr/include/sys/select.h:146,
                 from /usr/include/unistd.h:483,
                 from /usr/X11R7/include/X11/Xos.h:168,
                 from utils.c:79:
/usr/include/sys/signal.h:145: error: parse error before 'mcontext64_t'
/usr/include/sys/signal.h:177: error: parse error before 'ucontext64_t'
make[1]: *** [utils.lo] Error 1
make: *** [all-recursive] Error 1

My "workaround" was to add:

--- utils.c.orig	2006-11-02 11:13:02.000000000 +0100
+++ utils.c	2006-11-02 21:57:46.000000000 +0100
@@ -73,6 +73,10 @@
 #include <signal.h>
 #endif
 
+#ifdef __APPLE__
+#include <ucontext.h>
+#endif
+
 #if defined(WIN32) && !defined(__CYGWIN__)
 #include <X11/Xwinsock.h>
 #endif

Mac OS X 10.4.8
GCC 4.0.1
XORG_MAN_VERSION "Version 7.1.99.2"