Generate default values for the user-configurable CMake flags

[erlingrj]

This adds default values to the CMake flags which currently is passed over the command line when invoking cmake. This removes the need for:

1. Generating a .vscode/settings.json file to open and build generated sources in VScode.
2. The need for lfc to invoke cmake with all the flags
3. The need to generate CompileDefinitons.txt with the default values

Closing #1677

[erlingrj]

I am asking for your feedback here, @petervdonovan, since I believe you made the CMake integration and you might have some arguments for why we should not put the default flags in the generates CMakeLists.txt and instead pass them on the command line.

[petervdonovan]

I am in favor of this! IIRC we have discussed this as a group multiple times and collectively agreed that this is the right choice.

[lhstrh]

This looks nice!