Unable to install on debian about plan9port HOT 6 CLOSED

cd /usr/local/plan9/src/cmd/devdraw; mk all
9c -I/usr/include mklatinkbd.c
9l -o o.mklatinkbd mklatinkbd.o
./o.mklatinkbd -r $PLAN9/lib/keyboard | sed 's/, }/ }/' >latin1.h
9c -I/usr/include devdraw.c
9c -I/usr/include latin1.c
9c -I/usr/include mouseswap.c
9c -I/usr/include srv.c
9c -I/usr/include winsize.c
9l -o o.devdraw devdraw.o latin1.o mouseswap.o srv.o winsize.o x11-alloc.c x11-cload.c x11-draw.c x11-fill.c x11-get.c x11-keysym2ucs.c x11-load.c x11-pixelbits.c x11-screen.c x11-unload.c 
x11-alloc.c:1:10: fatal error: u.h: No such file or directory
    1 | #include <u.h>
      |          ^~~~~
compilation terminated.
x11-cload.c:1:10: fatal error: u.h: No such file or directory
    1 | #include <u.h>
      |          ^~~~~
compilation terminated.
x11-draw.c:1:10: fatal error: u.h: No such file or directory
    1 | #include <u.h>
      |          ^~~~~
compilation terminated.
x11-fill.c:1:10: fatal error: u.h: No such file or directory
    1 | #include <u.h>
      |          ^~~~~
compilation terminated.
x11-get.c:1:10: fatal error: u.h: No such file or directory
    1 | #include <u.h>
      |          ^~~~~
compilation terminated.
x11-load.c:1:10: fatal error: u.h: No such file or directory
    1 | #include <u.h>
      |          ^~~~~
compilation terminated.
x11-pixelbits.c:1:10: fatal error: u.h: No such file or directory
    1 | #include <u.h>
      |          ^~~~~
compilation terminated.
x11-screen.c:1:10: fatal error: u.h: No such file or directory
    1 | #include <u.h>
      |          ^~~~~
compilation terminated.
x11-unload.c:1:10: fatal error: u.h: No such file or directory
    1 | #include <u.h>
      |          ^~~~~
compilation terminated.

WSYSTYPE=x11
X11=/usr
X11H=-I/usr/include
CFLAGS=$CFLAGS -I/usr/include
HFILES=$HFILES $XHFILES
WSYSOFILES=$WSYSOFILES 
WSYSHFILES=x11-inc.h x11-keysym2ucs.h x11-memdraw.h

WSYSOFILES=$WSYSOFILES x11-alloc.o x11-cload.o x11-draw.o x11-fill.o x11-get.o x11-keysym2ucs.o x11-load.o x11-pixelbits.o x11-screen.o x11-unload.o