Bump c++ requirement and supported compilers

[drdanz]

According to our policies, we can now drop CMake 3.5 on the devel branch.

For reference this is a list of c++ features supported by each compiler: https://en.cppreference.com/w/cpp/compiler_support

• I think we can drop support for visual studio 2015. We don't have an explicit policy for that, but I think that supporting the 2 most recent versions is enough. Visual Studio 2015 already supported C++14 with a couple of exceptions, Visual studio 2017 fully supports C++14. I assume that, whatever visual studio version people is using, they will update it to the latest update.
• Debian stretch/oldstable has the oldes gcc compiler (6.3.0) which is not what I would like to support, but still supports all the C++14

Therefore I don't see any problem in switching to c++14

• As soon as we drop support for stretch, the oldest compiler becomes 7.3.0 that supports most C++17 with a very limited subset of features that are not supported. This option is, in my opinion, to be taken really seriously, due to the very important additions to the language and to the standard library introduced by the standard.

So the options are

• 👎 Stay on C++11
• 👍 C++14
• 🚀 C++17 without the unsupported features

This is an important decision because it will impact the robots, and all the other repositories, therefore we need to discuss this.

cc @lornat75 @pattacini @vtikha @traversaro @Nicogene @aerydna

[traversaro]

I think there are some missing words after 7.3.0 .

[drdanz]

Fixed, thanks

[drdanz]

The reason why this hasn't still be closed is because of the PC104.
I'm currently waiting to understand if there will be a new release of the image

[drdanz]

The new PC104 image has been released.
Anyway, YARP 3.3 will require c++14 only, we will change it to c++17 after the release

[PeterBowman]

Bug #1959 (apparently also affects Linux despite its current title) could take advantage of C++17's if constexpr.