builtin.sh is installed as a set of tools to stand in for specific
filesystem call to builtin commands.

for example if /bin/test is used, then builtin.sh will be loaded
and simply call the builtin function of the same name.

At this moment it is installed as the following commands:
/bin/[
/bin/command
/bin/echo
/bin/expr
/bin/getopts
/bin/read
/bin/test
/bin/umask
/bin/wait

If one of the following is replaced by the NetBSD equivalent, please
update the list, and remove this completly when it is not anymore
required.