As discussed, we don't want to build flex and bison ourselves. Rather we just assume they are installed, and try to find and use them from CMake.

Possible ways of installing them:
1) chocolatey https://chocolatey.org/packages/winflexbison
2) vcpkg (although ports don't contain them at the moment)
3) Using Qt Online installer, which would download and install the binaries (currently this does not exist).