When calling update_chroot with --nousepkg it is silly to always force a
rebuild of the cross toolchain. Change the test to work regardless of
whether binary packages are enabled by checking if anything needs to be
built from source.
Now this code can be shared with setup_board. Only required if
setup_board is called with --nousepkg which is rare to never but feels
like the correct thing to do. Alternatively setup_board could always
use binary packages (as it basically does now).
This replaces the cross-toolchain compile step in bootstrap_sdk and adds the
ability to build native toolchains using the cross toolchain. This is just
the first step towards actually providing the native toolchain in a container.
