Trying to build the current sources (amd64 port):

# ./build.sh -j 2 -x -T /src/nb/tools -O /src/nb/obj -D /src/nb/dst -R
/src/nb/rel -r release

....

cleandir ===> usr.bin/ktrace
--- cleanman ---
rm -f ktrace.cat1
--- cleandepend ---
rm -f .depend ktrace.d subr.d /src/new/src/usr.bin/ktrace/tags 
--- cleanobjs ---
rm -f ktrace.o subr.o  ktrace.ln subr.ln
--- cleanprog ---
rm -f a.out [Ee]rrs mklog core *.core .gdbinit ktrace
rm: ktrace: is a directory
--- cleandir-usr.sbin ---
--- cleandepend ---
--- cleandir-usr.bin ---
*** [cleanprog] Error code 1
1 error

nbmake: stopped in /src/new/src/usr.bin/ktrace
*** [cleandir-ktrace] Error code 2
1 error

I updated my src tree, no change.  I guess I'm doing something wrong here?

  -jm