[C++] Add support for #pragma GCC unroll v4

[Jason Merrill]

On Wed, Dec 20, 2017 at 9:20 AM, Eric Botcazou <ebotcazou@adacore.com> wrote:
>> This needs some C++ tests, particularly with templates and range-for.  I
>> suspect that using the pragma in a template will ICE.
>
> No, that wasn't the case, but the combination template/range-for was indeed
> not working; fixed by adding a 5th parameter to the RANGE_FOR_STMT node.

OK.

Jason