[clang] [Clang] Add wraps attribute (for granular integer overflow handling) (PR #86618)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

The C standard is small enough that if you comb through the C grammar carefully, you can probably come up with explicitly rules for all the important constructs, and verify they work.  There's probably still a long tail of weird interactions with current and future clang extensions, and the whole thing is still sort of fragile because it's built on undocumented rules for type sugar propagation, but maybe if we're careful enough with testing, we can solve most of the compatibility?

I'd still prefer to have a distinct canonical type.

https://github.com/llvm/llvm-project/pull/86618