cirrus.yml: Improve the windows_msys2_task

cirrus.yml: Improve the windows_msys2_task

There's no need to run a full-blown bash just to create a directory.
And we can skip the "cd build" each time by doing it once at the
beginning.

Additionally, let's exclude some targets (that we already compile-test
with MinGW in the gitlab jobs) from the build, since the build time of
this task is very long already (between 80 and 90 minutes).

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230208103046.618154-1-thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230228190653.1602033-14-alex.bennee@linaro.org>