build: disable C4267 conversion compiler warning

Disable "warning C4267: conversion from 'size_t' to 'int', possible
loss of data".  Many originate from our dependencies and their sheer
number drowns out other, more legitimate warnings.

PR-URL: https://github.com/nodejs/node/pull/11205


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>