SelectFromMainFile makes macro type-checker not see "types" defined in headers.

[phadej]

This seems like inherent limitation of SelectFromMainFile.

[edsko]

I guess this is more than just the macro type checker; if you SelectFromMainFile, and you use types defined in some of those headers, those types must somehow be available. Related to the prelude (#293), multiple headers in one library (#75), and multiple libraries (#294). Leaving this ticket open to remind ourselves that we need to worry about this also for macro type checking.