Boost default file name layout at least on Windows will now contain
the architecture bits (32 or 64) to help tools chose the right version
instead of having a random default that forces the user to specify
Boost_LIBRARYDIR if the default doesn't match their need (after
they got a link-time error, far too late, instead of a build time error,
as in this patch by default).

This patch will manage the new file name layout in addition to the previous
ones. It will also make FindBoost look for the version of the libraries
that match the architecture associated with the chosen generator.
This will mainly impact Windows users by allowing them to
not have to build for each arch separately and have to specify
Boost_LIBRARYDIR. Instead they can now just build all in the same
directory and FindBoost will link with the right libraries.

Fixes #17575