[CMake] warn if features used that require >cmake-x.y

[Hendrik Sattler]

Am 3. Juli 2015 20:23:26 MESZ, schrieb Alexander Neundorf <a.neundorf-work at gmx.net>:
>On Thursday, July 02, 2015 04:13:40 Stuermer, Michael  SP/HZA-ZSEP
>wrote:
>> Have a look at cmake_minimum_required() and cmake_policy(). I think
>with
>> these both it should be possible to verify you are using a cmake
>version
>> that provides all features which are required by your project.
>
>no, what he is talking about is the other way round.
>He wants to make sure nobody accidentially introduces cmake code which 
>requires a newer version of cmake than what cmake_minimum_required()
>states.
>
>I think that's really hard to implement, but it would be nice to have.

This would also involve all variables and properties and all find modules.

I'd say that the only way to make sure that it works with that version is to actually test it...

HS