`Homebrew::SimulateSystem.current_os` may be returning the host OS or
a simulated OS and we can't be sure which in this context. At the
moment, this is expected to be the host OS but that may change in the
future. It shouldn't matter on a technical level but using "host" in
these variable names may lead to confusion.
This replaces "host" in names with "current", as it more accurately
describes the information.
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