A very stupid (but basically the only) way to determine the HOST_OPERATING_SYSTEM like GNU does it.
Basically, use it like this:
//go:generate ostypes name
Where name is the name of your package (e.g., main).
Yeah. I'm that lazy that I didn't figure it out myself. OH WELL.
You'll live.
Access the result using the variable, 'HostOS'. (Obviously using a package prefix if needed.)