Cygwin isn’t standard Windows. fork() is not available unless you use
cygwin, which requires that your programs be GPL-compatible. I don’t
consider cygwin an acceptable requirement.
For compiling a fork-dependent codebase to generate a Windows binary,
another option is to use the Microsoft Services for Unix (“SFU”)
environment, which supports building Windows binaries from code that
uses fork().
SFU isn’t free, but it has a 120 day trial. And if it does work, I’d be
happy to donate a few copies for those involved in making building Ruby
binaries for the community.
http://www.microsoft.com/windows/sfu/
http://www.interopsystems.com/tools/
Hope this helps,
Lee