Fix build breakage with Node.js 10.0.0-10.9.0. (#833)
Fix build breakage with Node.js 10.0.0-10.9.0. (#833)

The five argument WriteUtf8() method was introduced in Node.js v10.0.0,
it doesn't exist in older 10.x releases.

Use the four argument overload and a bunch of pragmas to silence the
compiler warnings.

Fixes: https://github.com/nodejs/nan/issues/832
Refs: https://github.com/nodejs/nan/pull/825
nodejs/nan,nodejs/nan,nodejs/nan,nodejs/nan