This adds MSVC builds built on Linux using wine. This requires some
settings of tools and flags because the autotools support for MSVC is
naturally somewhat limited.
The advantage of this approach is that it is compatible with our
existing CI scripts, so there's no need to write a Windows CI script
(in PowerShell or similar). If we want to test building and running on
Windows native (e.g., as supported by Cirrus CI) we could still do this
in the future.
Another advantage of this approach is that contributors can simply use
the docker image if they need a MSVC installation in a non-Windows
environment.
This commit also improves the Dockerfile by grouping RUN commands
according to Docker docs:
https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#run
The experiment of using Nix Shell was not really successful. Most
notably, Nix uses a bunch of wrapper scripts around compilers, which
make the build much less "pure". This may be useful but it's exactly
not what we want for CI. In particular, this resulted in gcc being used
for the "clang" builds because a wrapper script redefined the CC env
variable.
This now builds a single docker image (Debian) for all architectures
that we test in CI on Linux.
Tim Ruffing
Pieter Wuille