Normative: Re-resolve unresolvable references on the global in PutValue.

Currently, JSC, V8, SM, and XS all *do not throw* on the following code,
contra spec:

```javascript
"use strict";
undeclared = (this.undeclared = 42);
```

This has been a bug in implementations for a decade
(https://bugzilla.mozilla.org/show_bug.cgi?id=605515), and is arguably
implementation reality not only for the web but for most
implementations.

This changes the spec to match the implemented re-resolution behavior.

Also see
- tc39#467
- tc39/test262#1964

spec.html

@@ -3821,10 +3821,14 @@ <h1>PutValue ( _V_, _W_ )</h1>
  1. If Type(_V_) is not Reference, throw a *ReferenceError* exception.
  1. Let _base_ be GetBase(_V_).
  1. If IsUnresolvableReference(_V_) is *true*, then
+ 1. Let _name_ be GetReferencedName(_V_).
  1. If IsStrictReference(_V_) is *true*, then
- 1. Throw a *ReferenceError* exception.
+ 1. Let _realm_ be the current Realm Record.
+ 1. Set _V_ to ? ResolveBinding(_realm_.[[GlobalEnv]], _name_).
+ 1. Assert: IsStrictReference(_V_) is *true*.
+ 1. If IsUnresolvableReference(_V_) is *true*, throw a *ReferenceError* exception.
  1. Let _globalObj_ be GetGlobalObject().
- 1. Return ? Set(_globalObj_, GetReferencedName(_V_), _W_, *false*).
+ 1. Return ? Set(_globalObj_, _name_, _W_, *false*).
  1. Else if IsPropertyReference(_V_) is *true*, then
  1. If HasPrimitiveBase(_V_) is *true*, then
  1. Assert: In this case, _base_ will never be *undefined* or *null*.