Enable actual build tests in Windows/Appveyor CI

[ianfixes]

Appveyor is running a null test right now as proof of concept. Replace with a build test

Build Matrix

macOS 64-bit JIT
Linux 32-bit JIT
MinGW 32-bit ---

How To Build

These builds need to be installed SDL2 framework/library.

MinGW32/MSYS

$ cd macemu/SheepShaver
$ make links
$ cd src/Windows
$ ../Unix/autogen.sh
$ make

also:
https://www.emaculation.com/doku.php/compiling_sheepshaver_basilisk