How to build a mac runnable under win xp?

as the title…

In your dreams, I’m afraid!

Well…

You cannot build a mac package or the mac executable on pc nor can you create a pc exe on mac.

That’s not quite true since you can legally run XP or Linux in a virtual machine. That’s why I use a Mac as my main development platform[1], as it allows me to easily reach across the three systems I need to support.

[1] I actually prefer OSX to Windows or Linux for day to day usage too, but that’s largely balanced by my preference for developing in Visual Studio vs. XCode.

You can certainly compile Windows exe/dlls directly in OSX using a cross-compiler version of MinGW (gcc for Windows). I don’t think the tools exist to go the other way, unless you had access to an OSX emulator/VM.