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>

common.gypi

@@ -186,6 +186,10 @@
         'BufferSecurityCheck': 'true',
         'ExceptionHandling': 0, # /EHsc
         'SuppressStartupBanner': 'true',
+        # 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.
+        'DisableSpecificWarnings': ['4267'],
         'WarnAsError': 'false',
       },
       'VCLibrarianTool': {