Work around Node environment variable bug

Work around nodejs/node#18463 by
detecting the conditions under which the bug occurs and
performing a simple operation that resets the error state
if necessary.

lib/EnvironmentPlugin.js

@@ -7,6 +7,9 @@
 
 const DefinePlugin = require("./DefinePlugin");
 
+const needsEnvVarFix = ["8", "9"].indexOf(process.versions.node.split(".")[0]) >= 0 &&
+	process.platform === "win32";
+
 class EnvironmentPlugin {
 	constructor(keys) {
 		if(Array.isArray(keys)) {
@@ -23,6 +26,13 @@ class EnvironmentPlugin {
 
 	apply(compiler) {
 		const definitions = this.keys.reduce((defs, key) => {
+			// TODO remove once the fix has made its way into Node 8.
+			// Work around https://github.com/nodejs/node/pull/18463,
+			// affecting Node 8 & 9 by performing an OS-level
+			// operation that always succeeds before reading
+			// environment variables:
+			if(needsEnvVarFix) require("os").cpus();
+
 			const value = process.env[key] !== undefined ? process.env[key] : this.defaultValues[key];
 
 			if(value === undefined) {