configure: on Windows minimum glib version must be 2.30

In the 2.7 release we stated in the ChangeLog that the
minimum glib version for Windows hosts was 2.30, but we
didn't update configure to enforce this because we were
very close to the release at the point where we noticed
the issue, and it only affected building the test suite.
We then forgot that we needed to do it. Fix the omission.

(The reason for the 2.30 requirement is use of
g_dir_make_tmp() -- our fallback implementation uses
mkdtemp(), which isn't available on Windows.)

Reported-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Message-id: 1491224655-5776-1-git-send-email-peter.maydell@linaro.org