On my OS X 10.7.1 with Xcode 4.2 and a WSYSTYPE=x11 parameter, INSTALL is generating the following output.
(...)
* Resetting /usr/local/plan9/config
* Compiler version:
gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.1.00)
* Running on Darwin: checking architecture...
x86-64 found.
>>> Using LOCAL.config options:
WSYSTYPE=x11
* Building everything (be patient)...
>>> cd /usr/local/plan9/src/cmd/venti/srv; mk clean
done
[ "$SYSNAME" != Darwin ] || ranlib ../lib/*.a
>>> cd /usr/local/plan9/src/libventi; mk nuke
rm -f *.[o] [o].out y.tab.[ch] /usr/local/plan9/lib/libventi.a
ranlib: can't open file: ../lib/*.a (No such file or directory)
mk: for i in ... : exit status=exit(1)
>>> cd /usr/local/plan9/src/cmd/rio; mk all
9l -o o.rio client.o color.o cursor.o error.o event.o grab.o key.o main.o manage.o menu.o rio.o -L/usr/X11R6/lib64/ -lXext -lX11
nm: no name list
nm: no name list
* Installing everything in /usr/local/plan9/bin...
>>> cd /usr/local/plan9/src/cmd/rio; mk -k install
9l -o o.rio client.o color.o cursor.o error.o event.o grab.o key.o main.o manage.o menu.o rio.o -L/usr/X11R6/lib64/ -lXext -lX11
nm: no name list
nm: no name list
* Cleaning up...
* Renaming hard-coded /usr/local/plan9 paths...
* Building web manual...
* Done.
(...)