deps,win: increase msvs_shard in gyp for V8

Increase the number of shards to divide v8_base into. This increases
the number of calls to cl.exe but decreases the number of files
compiled each time.

Fixes: https://github.com/nodejs/v8/issues/4
PR-URL: https://github.com/nodejs/node/pull/12184


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>