It looks like it's missing some files?

This is done via "make build"

while building lib/X11:

rm -f Context.o unshared/Context.o
gcc -c -ansi -Dasm=__asm    -I../.. -I../../exports/include
-DCSRG_BASED  -DFUNCPROTO=15 -DNARROWPROTO -DXTHREADS  -D_REENTRANT
-DXUSE_MTSAFE_API -DXNO_MTSAFE_PWDAPI  -DUSE_NBSD_THREADLIB
-DHAS_SNPRINTF -DLIBX11  -O2   Context.c -o unshared/Context.o
In file included from locking.h:41,
                 from Context.c:70:
../../exports/include/X11/Xthreads.h:204: threadlib.h: No such file or
directory
*** Error code 1

Stop.
make: stopped in /usr/xsrc/xfree/xc/lib/X11