global is undefined in a strict environment

The following code will be generated when using the es6-set polyfill in a Rollup IIFE build:

(function() {
  "use strict";

  var isImplemented = function() {
    // ...
  };
  /* eslint strict: "off" */
  var global = (function() {
    return this;
  })();

  if (!isImplemented()) {
    Object.defineProperty(global, "Set", {
      value: polyfill$1,
      configurable: true,
      enumerable: false,
      writable: true
    });
  }
})();

global will be undefined because of the "use strict";, and the error Object.defineProperty: argument is not an Object will be thrown.

Is the recommended solution to remove the "use strict";, or could perhaps the global implementation be changed to something along the lines of the implementation in core-js?

// https://github.com/zloirock/core-js/issues/86#issuecomment-115759028
var global =
  typeof window == "object" && window && window.Math == Math
    ? window
    : typeof self == "object" && self && self.Math == Math
    ? self
    : Function("return this")();

[zloirock]

@medikoo CSP is not an issue since in engines where it’s possible we check window and self before usage of Function constructor.

[mathiasbynens]

I’ll just leave this here: https://mathiasbynens.be/notes/globalthis