lib: support setting process.env.TZ on windows

Fixes: https://github.com/nodejs/node/issues/4230


Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/38642


Reviewed-By: Steven R Loomis <srloomis@us.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>