[llvm] [StackColoring] Delete dead stack slots (PR #72633)

[Nikita Popov via llvm-commits]

nikic wrote:

There is an assertion failure in llvm/test/DebugInfo/COFF/lexicalblock.ll:
```
MachineFrameInfo.h:530: int64_t llvm::MachineFrameInfo::getObjectOffset(int) const: Assertion `!isDeadObjectIndex(ObjectIdx) && "Getting frame offset for a dead object?"' failed.
```

https://github.com/llvm/llvm-project/pull/72633