libc: fix daylight saving time handling
The algorithm computing daylight saving time incorrectly adds a day for
each month after January for leap years. The clock shift from/to DST can
be delayed if the last Sunday of a transition month is exactly seven
days before the first of the following month.
This change adds a day for the February month only.
Signed-off-by: Guillaume Bourcier <guillaumebourcier@free.fr>
Signed-off-by: Richard Braun <rbraun@sceen.net>
Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>