Pull request: Raise SIGFPE instead of abort in __gmp_exception`

[Yichao Yu]

> Patch checked in now.

I guess I'm not familiar with hg/gmp work flow. Is checked in
different from commited to the repo? I don't see the change appearing
in the repo[1] and my local fresh clone doesn't have it either.

[1] https://gmplib.org/repo/gmp/

>
> Regards,
> /Niels
>
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