* This new meta-component instructs BoostConfig.cmake to parse its
parent-directory for installed Boost components and will provide
imported targets for them as if they were listed as components in the
call to `find_package`.
* If this new component is used it has to be the only component
provided to the `find_package` call.
* If another component is provided together with the "ALL" component a
non-fatal error will be triggered (with a hint for how to fix that
error) but the script will continue looking for all components,
ignoring that additional component.
However, as typical for non-fatal errors CMake configuration will
still fail in the end.
* If BoostConfig.cmake was triggered by FindBoost.cmake with that
meta-component it will continue to work as if `find_package` was
called in config mode, but FindBoost.cmake might print a warning if
either `Boost_DEBUG` or `Boost_VERBOSE` was set.
