tools: allow people to compile w/out configuring

It's useful to be able to build up the host tools without having to select
a board first.  Pretty much all tools in there are config-independent
anyways.

Also add a shortcut "tools-all" to quickly build all host tools that are
actually config-independent to allow for simple test builds.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>