Make nested preprocessor IFs work

[bowbahdoe]

Added a basic preprocessor, but it will misbehave if conditions are nested. That isn't a problem right now but it might be worth tackling before someone foot guns

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label, comment or add the valid label or this will be closed in 5 days.

[bowbahdoe]

This is not really a priority anymore since this preprocessor was removed