Migrate build system to CMake

[miurahr]

There were initiatives to migrate build system to CMake in 2012-2013, CMAKE4GDAL project. I have now been developing a build configuration on CMake that continues CMake4Gdal project ​https://github.com/miurahr/gdal/commits/compile_with_cmake

I do it because it seems to be a good chance to challenge again. There are a couple of reasons.

• Microsoft Visual Studio 2017 support CMake. ​https://blogs.msdn.microsoft.com/vcblog/2016/10/05/cmake-support-in-visual-studio/

• Jetbrains CLion also support only CMake. ​https://www.jetbrains.com/clion/ (This is my motivation)

• CMake support gcc, clang, mingw and VC++

• CMake support GNU Make(Linux), Ninja(VS/Windows), nmake(VC++), XCode(mac)

Other merits we will get after successfully migrating to CMake on all platforms

• Incremental compile and test that improve productivity

• Out-of-source compile that help Appvoyer / Travis CI tests speedy, developers can test it in multiple options.

• Single build configuration for all platforms.

Demerit

• There are not enough documentation for CMake.

• We are not fluent for CMake now.

So migrating to CMake should be considered carefully. I'd like to propose a step-by-step migration strategy.

1. Develop CMake configuration on topic branch or github project.

2. Merge CMake build configuration co-existence with GNU Make and VC configurations. (2.3 or 2.4) and add CI test on Travis / Appvoyer for cmake. Now it is a state of a technical preview. Still team will release binaries building with legacy build system. At this time, all contributor should aware that he/she should update both cmake and legacy one.

3. Drop legacy build system when every core developers satisfy CMake/IDE experiences. (3.0 or 4.0)