There is no tm_gmtoff member in 'struct tm' on Windows.
Update rtc-test.c and m48t59-test.c accordingly.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20220824094029.1634519-16-bmeng.cn@gmail.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>