build.sh can be subsumed by CMake

[eyalroz]

Essentially all of the functionality in build.sh can be achieved in a relatively straightforward manner using just CMake's infrastructure. ccmake can be used to browse the various options, their descriptions and possible values, and the CMake configuration (as opposed to the generation) step can include the validity checks.

This would:

• Reduce the amount of code and text
• Simplify the CMakeLists.txt file somewhat
• make it easier to adopt some modern CMake idioms
• make it easiert to use CMake for installing the engine rather than just building
• Enable CMake config-file-based dependency management where the engine is a dependency

[bernhardmgruber]

I just encountered a similar situation. The current workflow using build.sh does not play well with CMake supporting IDEs like Visual Studio or CLion, because these basically just invoke cmake and then infer the project settings from the CMakeCache or similar. With the current setup, no targets are enabled and there are also no options to configure through the IDE or cmake-gui.