Er, er, just as the original comment:
if compiling for Windows, use this separate set
(too difficult to ifdef all the autoconf defines)

For windows, or Android (yes, its linux), there is no necessary to run configure.
As for windows or android, usually there is no autoconf, no way to run configure.
There is NMakefile, windows users can just run `nmake', which is part of Microsoft Visual Studio.
In that days I even wanted to provided a Microsoft Visual Studio project file, however, I didn't.

And when I check the original fping, there is linux.h.
So it should be better to split them from fping.c to win32.h, just as:
https://github.com/liudongmiao/fping-win32/commit/9d226a57910627cd111b47724e24988d65cdd7d5

However, currently autoconf/configure is used to generate version number too.
So there should somewhere to define version number if we dont want to autoconf.
// actually, there is predefine version number in autoconf/configure too.