closure-compiler: Undocumented breaking change in v20170423: missing externs?

Reported in https://github.com/alexeagle/closure-compiler-angular-bundling/issues/30#issuecomment-300364464:

Upgrading from v20170409 to v20170423 breaks my program:

node_modules/@angular/core/@angular/core.js:5607: ERROR - variable System is undeclared
        return System.import(module)
               ^^^^^^

node_modules/@angular/platform-browser/@angular/platform-browser.js:3091: ERROR - variable Hammer is undeclared
        const /** @type {?} */ mc = new Hammer(element);
                                        ^^^^^^

node_modules/moment/moment.js:8: ERROR - variable module is undeclared
    typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
                                          ^^^^^^

node_modules/moment/moment.js:9: ERROR - variable define is undeclared
    typeof define === 'function' && define.amd ? define(factory) :
           ^^^^^^

node_modules/moment/moment.js:399: ERROR - variable require is undeclared
                require('./locale/' + name);
                ^^^^^^^

node_modules/rxjs/util/root.js:8: ERROR - variable global is undeclared
else if (typeof global == 'object' && global.global === global) {
                ^^^^^^