Recently used cmake-gui locations are searched only on Windows because
the Windows registry is used to record the values. This behavior is
historical and may be removed by a policy in the future so rather than
implementing it on other platforms simply document the current behavior.
These documents were represented in the builtin documentation using a
common starting point with placeholders substituted by each command.
Convert them back to this approach using the reStructuredText include
directive and substitutions to avoid duplication.