[cmake-developers] Add command line options for deprecation message control

[Michael Scott]

> What is the difference between the intended uses of those existing options
> and the intended uses of the new options, given that -Wno-dev is mostly
> useful for third parties to silence policy warnings?

Working on this issue, I did find the different variables/options a bit confusing. dev and deprecated both change the effect of message modes, pretty much doing the same thing but slightly different (for example there is -Wdev and -Wno-dev, but not -Werror=dev or -Wno-error=dev). Would it be worth refactoring the -W dev options to be in line with the -W deprecated options?

> If the new options are merged to master should -Wdev and -Wno-dev also be
> changed to affect CMAKE_WARN_DEPRECATED?

That would be sensible behaviour to me, shall I modify cmake::Configure to do this?

Cheers,
Michael