Was unconditionally throwing "Function constructor not supported".
Now js-function-ctor joins param strings with commas, wraps the
body in (function(<params>){<body>}), and runs it through js-eval.
Now Function('a', 'b', 'return a + b')(3,4) === 7.
built-ins/Function: 0/14 → 4/14. conformance.sh: 148/148.