Make large enum constants unsigned, revisited

[Frank Ch. Eigler]

Hi, Alan -

On Wed, Mar 02, 2016 at 03:16:01PM +1030, Alan Modra wrote:
> The patch at https://sourceware.org/ml/cgen/2014-q2/msg00008.html was
> never committed, presumably because the submitter gave up trying.  [...]

Yikes.  Anyway lgtm, go for it.

- FChE