In strict mode code, attempts to assign to an unresolvable reference must throw a ReferenceError exception. Fixes gh-1964

test/language/identifier-resolution/assign-to-global-undefined.js

@@ -0,0 +1,20 @@
+// Copyright (C) 2020 Rick Waldron. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-initializeboundname
+description: >
+  In strict mode code, attempts to assign to an unresolvable reference must throw a ReferenceError exception
+info: |
+  via sec-putvalue
+
+  If IsUnresolvableReference(V) is true, then
+    If IsStrictReference(V) is true, then
+      Throw a ReferenceError exception.
+
+flags: [onlyStrict]
+negative:
+  phase: runtime
+  type: ReferenceError
+---*/
+
+undeclared = (this.undeclared = 5);