Sometimes figuring what differs between platforms is useful to fix
build issues, to decide what ifdef to add for example. Let's always
call $CC -dM -E- before starting make.
This patch cleans up the Windows CI to look more similar to the refactored
Linux CI on GitHub Actions.
It switches the environment set-up from some manual cygwin setup via choco to
the msys2/setup-msys2@v2 action which just works and allows later steps to look
like any others without need to manually specify the shell.
This new setup is much faster than before where a single Windows build required
more than 10 minutes with more than 5 minutes just spent setting up the
environment and more than 6 minutes compiling HAProxy.
With this patch the setting of of the environment is done in less than a minute
and HAProxy is compiled in less than 2 minutes.
The only drawback is that Lua does not appear to be readily available. I expect
this to be acceptable and that the benefits far outweight this small drawback.
