Need CI on windows / mingw

[vondele]

See d7a2689#commitcomment-41319808

[ppigazzini]

AppVeyor and Travis CI provide msys2.
https://www.appveyor.com/docs/windows-images-software/#mingw-msys-cygwin
https://docs.travis-ci.com/user/reference/windows/

[niklasf]

Yet another option would be GitHub actions.

For example, here is a workflow to build binaries for a bunch of different flavors of x86 Linux (gcc), aarch64 Linux, x86 Windows (MINGW), x86 macOS and Apple Silicon: https://github.com/niklasf/Stockfish/blob/fishnet-master/.github/workflows/build.yml

(clang on Linux and MSVC on Windows are also supported, but not included in that particular script, because only one compiler each is needed for its purpose.)

[vondele]

now that we have github actions in place, this issue could be fixed.

[ppigazzini]

Info about GitHub Actions and mingw-w64:

• Supported SW on hosted runners : Windows hosted runners have already installed msys2 (first setup, no packages) and mingw-w64 8.10, there is also chocolatey
• setup-msys2 action : info and examples:
  • msys2 workflow : the workflow used by msys2 project to test and upload the msys2 packages
  • GitHub Actions with msys2 : some simple examples

EDIT_000: the msys2 project workflow is installing the complete toolchain (all programming languages) for each environment, if this is too slow we could simplify a lot because to build SF are required only make (from msys environment) and the gcc for each environment (eg mingw-w64-x86_64-gcc for mingw-w64 environment, see https://www.msys2.org/docs/environments/)