Highlights are:
- Since MSYS2 is much more unixlike than our old build environment we
can remove most Windows specific hacks from the Makefile.
- MSYS2 has an package manager, the build environment can be updated
by "pacman -Syu" just like an ordenary Arch Linux installation.
- Parallel builds are now working.
- git is integrated into the build envirment.
- zlib is now linked as a dynamic lib.
After this commit the old bild environment will no longer work! The
latest version must be downloaded and extracted to C:\MSYS2. Get it
here: https://deponie.yamagi.org/quake2/windows/build/
After some long discussions it was realizied that the old README had way
too much informations and was too unspecified on some topics. This new
README was written from scratch and focus on installing Quake II.
