[dmd-internals] Two regression patches

[Walter Bright]

Done. Thanks!

Don Clugston wrote:
> There are currently ten regressions from 2.030 and later. There are
> patches for two of them:
>
> 4516 Regression(2.040): forward declaration of enum not supported
>
> The patch for
> 4503  forward reference to aliased template instance
> also fixes
> 3679 Regression(2.031) template forward reference regression
> 4267 forward reference error when 2-fold aliasing a template instance
>
> I've also made a mitigation patch to change this wrong-code into an
> unimportant rejects-valid:
> 3326 $ in delegate literal causes Access Violation
>
>