src/vs/workbench/services/configurationResolver/common/variableResolver.ts/AbstractVariableResolverService/prepareEnv
class AbstractVariableResolverService:	private prepareEnv(envVariables: IProcessEnvironment): IProcessEnvironment {
		// windows env variables are case insensitive
		if (isWindows) {
			const ev: IProcessEnvironment = Object.create(null);
			Object.keys(envVariables).forEach(key => {
				ev[key.toLowerCase()] = envVariables[key];
			});
			return ev;
		}
		return envVariables;
	}