[llvm] [InferAS] Infer the address space of inttoptr (PR #173244)

[Luo Yuanke via llvm-commits]

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LuoYuanke wrote:

Introducing `mutable` to member `PtrIntCastPairs` is to avoid changing each member method of `InferAddressSpacesImpl` who calls `getIntToPtrPointerOperand()` which modify `PtrIntCastPairs`.

https://github.com/llvm/llvm-project/pull/173244