I tried building xorg-server 6.9.0nb14 (as part of monolithic xorg)
using pkg_comp on a 4.0 machine.  The 4.0 build sets are from July 2.
The build failed:

cc -o Xprt -O2 -fno-strict-aliasing -ansi -Dasm=__asm -Wall -Wpointer-arith -Wstrict-prototypes                           -Wmissing-prototypes -Wmissing-declarations            
         -Wredundant-decls -Wnested-externs -Wundef     -L/pkg_comp/obj/pkgsrc/x11/xorg-server/default/xc/exports/lib   Xprint/ddxInit.o Xprint/dpmsstubs.o Xprint/miinitext.o   
      os/libcwrapper.o dix/libdix.a os/libos.a  Xprint/libprinter.a       Xprint/raster/libraster.a Xprint/pcl/libpcl.a Xprint/pcl-mono/libpcl.a Xprint/ps/libps.a mfb/libmfb.a c
fb/libcfb.a            cfb32/libcfb32.a mfb/libmfb.a dix/libxpstubs.a mi/libmi.a composite/libcomposite.a damageext/libdamage.a miext/damage/libdamage.a xfixes/libxfixes.a miext
/cw/libcw.a                   Xext/libexts.a xkb/libxkb.a os/libos.a Xi/libxinput.a                   lbx/liblbx.a                   /pkg_comp/obj/pkgsrc/x11/xorg-server/default
/xc/lib/lbxutil/liblbxutil.a  randr/librandr.a render/librender.a Xext/libext.a dbe/libdbe.a record/librecord.a GL/glx/libglx.a                GL/mesa/GLcore/libGLcore.a XTrap/l
ibxtrap.a -L/usr/pkg/xorg/lib    /pkg_comp/obj/pkgsrc/x11/xorg-server/default/xc/lib/font/libXfont.a -L/pkg_comp/obj/pkgsrc/x11/xorg-server/default/.buildlink/lib -Wl,-R /pkg_co
mp/obj/pkgsrc/x11/xorg-server/default/.buildlink/lib -lfreetype dix/libxpstubs.a  -L/usr/lib -Wl,-R/usr/lib -lz -lm                  -lXau -lXdmcp -li386 -lX11 -L/usr/pkg/lib -L
/usr/pkg/xorg/lib  -Wl,-R/usr/pkg/lib  -Wl,-R/usr/pkg/xorg/lib
Xprint/ps/libps.a(psout_ftpstype1.o): In function `PsOut_DownloadFreeType1':
psout_ftpstype1.c:(.text+0x64): warning: warning: tempnam() possibly used unsafely, use mkstemp() or mkdtemp()
/pkg_comp/obj/pkgsrc/x11/xorg-server/default/xc/lib/font/libXfont.a(fttools.o): In function `FTcheckForTTCName':
fttools.c:(.text+0xc5): undefined reference to `ft_isdigit'
*** Error code 1

Stop.
make: stopped in /pkg_comp/obj/pkgsrc/x11/xorg-server/default/xc/programs/Xserver
*** Error code 1

Stop.
make: stopped in /usr/pkgsrc/x11/xorg-server
*** Error code 1



		--Steve Bellovin, http://www.cs.columbia.edu/~smb