mingw32_HOST_OS support

[moodmosaic]

Prelude

@jacobstanley wrote recently this article that became popular in the property-testing community, combining hedgehog, test data that has foreign key references, and tmp-postgres (among others).

I've put up an example repo with the source code from the article, and the only issue I've found is that
tmp-postgres won't build under Windows (mingw32_HOST_OS) because of the unix dependency.

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Is it worth trying @pmlodawski's signal or similar to have tmp-postgres compile also on Windows? If that turns out to be realistic, would you accept a pull request?

As far as I can tell, tmp-postgres relies on unix mostly (if not only) for stopping the Postgres process.

[jfischoff]

I'll accept a pull request. I have not done this because I don't have a windows machine myself.