Status of Posix on Windows

I'm currently using a Mac.
The recent discussion about the "embed" directive inspired me to find a solution to the problem of embedding a directory in an ANSI C program, of course without a modern compiler. You can see my proposal at
http://malcolmmclean.github.io/babyxrc/importingdirectories.html
(It's in the babyxrc documentation on github if this link doesn't work)
The program directorytoxml crawls a diectory and converts it to XML. And
it can't be written in ANSI C. It has to use Posix. The question is whether this in in practise portable to Windows, or if I need to dust off a Windows machine and write a Windows version using FindFirstFile and FindNextFile.
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Check out Basic Algorithms and my other books:
https://www.lulu.com/spotlight/bgy1mm