[Bug target/79173] add-with-carry and subtract-with-borrow support (x86_64 and others)

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79173
Bug 79173 depends on bug 80491, which changed state.

Bug 80491 Summary: [7 Regression] Compiler regression for long-add case.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80491

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---