struct tm -> std::tm, memset of tm goes to {} (#1079)

struct tm -> std::tm, memset of tm goes to {} (#1079)

* struct tm -> std::tm, memset of tm goes to {}.

* init std::tm related variables.

tidy found found the following warnigns related to our usage of
std::tm:
cppcoreguidelines-pro-type-member-init
and std::tm*:
cppcoreguidelines-init-variables

* make GPS_D600_Get var tm automatic storage duration

and intialize it.