[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 #4 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> 
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Patch applied to trunk.  Not sure if we want to backport or not, so leaving
open just in case.