runtime - class inheritance pattern not compatible with frozen intrinsics

it is becoming increasingly common to freeze javascript intrinsics (Object, Array...) (see nodejs, endo/ses, xs)

while this is generally not an issue for packages that do not extend intrinsics, there are a few unfortunate side effects due to javascript's "override mistake", namely obj.constructor = ... fails due to the inherited property "constructor" being read-only on Object.prototype

here is the inheritance pattern at fault

regenerator/packages/regenerator-runtime/runtime.js

Lines 105 to 106 in 0c2aba1

    
           GeneratorFunction.prototype = Gp.constructor = GeneratorFunctionPrototype; 
        
           GeneratorFunctionPrototype.constructor = GeneratorFunction;

here is a compatible inheritance pattern
https://github.com/isaacs/inherits/blob/9a2c29400c6d491e0b7beefe0c32efa3b462545d/inherits_browser.js#L6-L13
alternatively you can just use defineProperty instead of assignment

reproduction steps:

Object.freeze(Object.prototype)
require('./runtime.js')

fix is ready here ---> #411

	GeneratorFunction.prototype = Gp.constructor = GeneratorFunctionPrototype;
	GeneratorFunctionPrototype.constructor = GeneratorFunction;