Auto merge of #98627 - RalfJung:interpret-arith, r=lcnr

interpret: don't rely on ScalarPair for overflowed arithmetic

This is for rust-lang/rust#97861.
Cc `@eddyb`

I would like to avoid making this depend on `dest.layout.abi` to avoid a branch that we are not usually covering both sides of. Though OTOH this seems like fairly straight-forward code. But let's benchmark this option first to see how bad that extra `force_allocation` really is.

Author: bors