v8: use correct timezone information on Solaris

`timezone` variable contains the difference, in seconds, between UTC and
local standard time (see `man 3 localtime` on Solaris).

Call to `tzset` is required to apply contents of `TZ` variable to
`timezone` variable.

BUG=v8:2064

Review URL: https://chromiumcodereview.appspot.com/10967066
Patch from Maciej Małecki <me@mmalecki.com>.

This is a back-port of upstream commit r12802.