relaylog: use threadsafe localtime_r
relaylog: use threadsafe localtime_r

Don't know why, but it seems I was totally on a single-threaded planet
when I used localtime() here.  Avoid a race here, and use localtime_r
with a stack allocated struct tm.

grobian/carbon-c-relay,piotr1212/carbon-c-relay,piotr1212/carbon-c-relay,grobian/carbon-c-relay,piotr1212/carbon-c-relay,grobian/carbon-c-relay,piotr1212/carbon-c-relay