The makefile in share/man/man8/man8.sparc sets the search path to include 
sys/arch/sparc/...  This fails badly if you don't sup that particular part 
of the build system (I only want an ARM32 build).

all ===> man/man8/man8.sparc
nroff -mandoc /work/rearnsha/netbsd/share/man/man8/man8.sparc/MAKEDEV.8 > 
MAKEDEV.cat8
nroff -mandoc /work/rearnsha/netbsd/share/man/man8/man8.sparc/boot.8 > 
boot.cat8
make: don't know how to make installboot.8. Stop
*** Error code 2

If this man page must live in the sys/arch/sparc area, the rules should 
test for the presence of this dir before trying to build installboot.8