[llvm] [CodeGen] Fix handling dead redefs in finalizeBundle (PR #157427)

[Jay Foad via llvm-commits]

jayfoad wrote:

AMDGPU backend uses BUNDLEs for things that definitely need to execute serially e.g.:
```
$ grep -A4 BUNDLE test/CodeGen/AMDGPU/insert-waitcnts-crash.ll
  ; CHECK-NEXT:   BUNDLE implicit-def $sgpr16_sgpr17, implicit-def $sgpr16, implicit-def $scc, implicit-def $sgpr17 {
  ; CHECK-NEXT:     $sgpr16_sgpr17 = S_GETPC_B64
  ; CHECK-NEXT:     $sgpr16 = S_ADD_U32 internal $sgpr16, target-flags(amdgpu-gotprel32-lo) @bar + 4, implicit-def $scc
  ; CHECK-NEXT:     $sgpr17 = S_ADDC_U32 internal $sgpr17, target-flags(amdgpu-gotprel32-hi) @bar + 12, implicit-def $scc, implicit internal $scc
  ; CHECK-NEXT:   }
```

https://github.com/llvm/llvm-project/pull/157427