Auto merge of #145144 - scottmcm:unsigned_overflow_intr, r=nikic

Stop using uadd.with.overflow

As discussed in [#t-compiler/llvm > &rust-lang#96;uadd.with.overflow&rust-lang#96; (again) @ 💬](https://rust-lang.zulipchat.com/#narrow/channel/187780-t-compiler.2Fllvm/topic/.60uadd.2Ewith.2Eoverflow.60.20.28again.29/near/533041085), stop emitting `uadd.with.overflow` in favour of `add`+`icmp` instead.

r? nikic

Author: bors