Modern CMake

[Srykah]

Several CMake files and commands feature strongly discouraged uses of CMake : for example, in-source builds and GLOB variables for listing sources.

We should update CMake's usage to modern CMake where possible (for example following those guidelines) ; in the long term, we should try and use CTest and CPack as well.

[milkyroute]

It would be great, but I have really few notions of CMake, everything has been done by @BAKFR. I think it's better to see this with him, if he's still available. Otherwise, I'm sorry but I won't be able to help a lot on this.