Throwing a string does not report correctly

[ljharb]

A file of:

throw new Error('foo');

provides these results:

#### ch
Error: foo

#### v8
Error: foo

#### sm
Error: foo

#### jsc
Error: foo

A file of:

throw 'foo';

provides these results:

#### ch
foo: undefined

#### sm


#### v8
foo: undefined

#### jsc
foo: undefined

This is both unclear that it threw, but also, spidermonkey is reporting the wrong result.