output/csv: use intermediate time_t var, silence compiler warning

output/csv: use intermediate time_t var, silence compiler warning

There are platforms where timeval and time_t disagree on the width of
the data type of the field which holds seconds. Passing a pointer to an
unexpected type results in warnings (and probably unreliable execution).

Assign the value which is gotten from a timeval to an intermediate
time_t variable, so that the ctime() invocation becomes portable.