Previously core itself was the library containing the code to gather
common information (build info, CPU info, and OS info), however all of
this isn't core-dependent and can be moved to the common code and use
the common interfaces. We can then just call those functions from the
core instead.

This will allow replacing our CPU detection with Xbyak's which has
better detection facilities than ours. It also keeps more
architecture-dependent code in common instead of core.

We can just take the value parameter by value which allows both moving
into it, and copies at the same time, depending on the calling code.

These operators don't modify internal class state, so they can be made
const member functions. While we're at it, drop the unnecessary inline
keywords. Member functions that are defined in the class declaration are
already inline by default.

This provides the equivalent behavior, but without as much boilerplate.
While we're at it, explicitly default the move constructor, since we
have a move-assignment operator defined.