It's not perfect, but I honestly just can't be arsed to figure out
how to use the Windows API to do the same thing that pwd.h does.
At the very least, Starfighter can now be successfully compiled for
Windows with MinGW simply by defining the "SF_WINDOWS" environment
variable to 1 (or any other non-empty value). The only downside is
that it uses the current working directory to decide where
.config/starfighter should go, meaning it can't be installed into
restricted directories like Program Files.