Add cmake support for compiler bootstrap

[aleksisch]

This PR introduces cmake support to conveniently bootstrap compiler in a future.
Since we're adding standalone contexts and rewrite some parts of compiler to das we need to be able to build it (das files useless without das compiler).

1. First we need to create das compiler from available .cpp and .h files. I wasn't able to find a good way to do it in CMake without copy, so all generated files will be copied to build folder (to ignore the fact that they are generated).
2. Build stage0 compiler from this files (target daslang-stage0)
3. Later on we will use this compiler for transpilation of das files into cpp.
4. Transpile all required files (daslib & standalone contexts) to cpp and build regular daslang
5. Enjoy

In future we may want to automatically update target daslang-stage0 if files, which responsible for transpilation are changed to be always up to date (right now it's only ast_aot_cpp.cpp).