Windows build instructions out of date

[sbmcvey79]

Hi,
The windows build instructions call for msys mingw32 which is being phased out and many of the things needed are no longer available in pacboy. It would be helpful to me at least to have cleaner Windows build instructions.

[Sonic-Amiga]

Hello! I also tried to build under modern MInGW64, and it failed with:
Required package 'libudev' not installed
Required package 'libmagic' not installed
Required package 'mbedtls' not installed
build/ab.mk:122: .obj/unix/build.targets: No such file or directory
I did install imagemagick and mbedtls; and there's no udev on mingw. It apparently fails to recognize Windows.

[Sonic-Amiga]

UPD: After updating my installation everything went well like a charm. You need to type "make BUILDTYPE=windows", autodetection doesn't work properly.

[Sonic-Amiga]

Fix: #857

[davidgiven]

That last was actually intentional, to allow cross compilation from WSL (where Windows autodetection doesn't work, and where you might want a Unix build or a Windows build depending on what you're doing). However, I don't think anyone actually uses this and it's clearly confusing so let's just autodetect it. It's easy enough to override BUILDTYPE for people who know what they're doing.

[Sonic-Amiga]

Well, cross compilation is cross compilation, that's not a default scenario, so you should know what you're doing.
BTW, with the merged patch behavior on WSL will stay the same as it was before (i. e. default to Linux)