The most likely documentation page a project author will read in
response to a policy warning is the page for the policy itself.
Add to every policy documentation page a note explicitly stating
that the OLD behavior is deprecated. Also mention this in the
cmake_policy() command documentation that explains how to set a
policy to OLD.
Suggested-by: Fraser Hutchison <fraser.hutchison@gmail.com>
The previous example for CMP0054 did not show how critical the policy is
since the result is the same in both cases (NEW and OLD behavior).
Instead show an example when the policy does make a difference.