[Bug middle-end/82547] wide_int is not setting overflow properly for large unsigned add/subtract calculations.

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82547

--- Comment #2 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> 
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Created attachment 42675
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42675&action=edit
Candidate patch

Here's the patch I'm testing.