ImportC can now automatically run the preprocessor

[rikki cattermole]

On 16/05/2022 5:16 PM, max haughton wrote:
> As long as the semantic analysis can happen in a new Scope (a dmd one 
> not a lexical one) then the normal semantic routines should work and 
> it'll be the same as any other mixin (I.e. mixin is not free of bugs).

Indeed, we already have scope awareness of C vs D. As long as we can mix 
them (within each other) than shouldn't need things to be redone.

It shouldn't be any different than:

void main() {
	writeln;

	{
		... c ...
	}

	writeln;
}