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

[Michael Scott]

> Let's start with the toggle because that will make cmake-gui able
> to set the option just like the command line.
Sounds good, that's what I was thinking as well.

> Also I'm not sure what to do about persistence of the option check
> boxes in cmake-gui when selecting a different build tree.  As a user
> I may expect those options to be loaded from the current cache in each
> build tree I select.
The build tree is selected by changing the source directory setting in 
the GUI right? So it should get the state of the checkboxes based on the 
cache whenever this changes.

Adding in one toggle would be fine, but I imagine that when we come to 
adding support for upgrading warnings to errors, the additional two 
checkboxes would be a bit much. I was thinking of perhaps instead having 
just one entry in the options menu, which opens up a sub-window which 
contains the group of message related options.

Cheers,
Michale