[wide-int] small cleanup in wide-int.*

[Mike Stump]

On Dec 3, 2013, at 8:52 AM, Richard Sandiford <rsandifo@linux.vnet.ibm.com> wrote:
> You probably already realise this, but for avoidance of doubt, Richard
> was also asking that we reduce MAX_BITSIZE_MODE_ANY_INT to 128 on x86_64,
> since that's the largest scalar_mode_supported_p mode.

Personally, I'd love to see scalar_mode_supported_p be auto-generated from the gen*.c programs; then, we could just add a line to that program to synthesize this value.  Absent that, which I think is a nice long term direction to shoot for, we'd need yet another #define for the target to explain the largest supported size.