process.binding() is deprecated. When running recent versions of Node.js
with --pending-deprecation, the current code results in a printed
warning about process.binding() usage. process.binding() is used to
create writev(), but Node.js now exposes fs.writev(). Use that instead
when it exists. Otherwise, fall back to the polyfill. This will avoid
runtime deprecation messages for end users.

If the minimum supported engine is ever Node.js 12.9.0 or above, the
polyfill code should be removable at that time.