[Bf-committers] CMake version bump for master branch

[Campbell Barton]

Hi, recently we agreed to bump CMake to 3.5 in the blender2.8 branch [1],
I'm proposing to bump the version requirement in master to 3.5 as
well, to take advantage of newer CMake features without causing
unnecessary conflicts.

While there are no urgent features we need from a newer version, the
way we link libraries is quite hacky and hard to understand (see:
BLENDER_SORTED_LIBS in build_files/cmake/macros.cmake) - which can be
resolved in 3.1 or newer [2]

[1]: https://lists.blender.org/pipermail/bf-committers/2017-August/048648.html
[2]: https://developer.blender.org/T46725

-- 
- Campbell