The Windows version is now built using the excellent MSYS2 distribution. This distributions contains updated version of all requirements for FS-UAE and (almost) all requirements for FS-UAE Launcher & Arcade, including a Python version compiled with mingw. The end result is a build environment which is much easier to set up and use. I even made an easy-to-follow step by step tutorial for installing this environment and compiling the git version of FS-UAE on Windows. But, there is always a chance that the changes have introduced bugs in FS-UAE or FS-UAE Launcher, so please let me know if something which worked in 2.5.20dev is broken in 2.5.21dev.
The OS X build environment has also been updated with newer library versions – so same here, please report any new issues in 2.5.21.dev, if any.