Fix daylight savings code on Windows altogether

Reverted the previous change, the local timezone adjustment should not include
the daylight savings, because in a long running program that runs across the
DST boundary, the timezone doesn't change, but the DST adjustment does. That
is why LocalTZA is always used in conjunction with a call to DaylightSavingTA,
which unfortunately had a silly bug on Windows:

It was assumed that _localtime64_s returns zero on failure, similar to
localtime_r on Unix. However it is exactly the opposite, zero is returned
on success and an error code is returned on failure.

Change-Id: Ib324f09f290870630b66793882c5b121de445f05
Reviewed-by: Lars Knoll <lars.knoll@digia.com>