[llvm] [StackSafetyAnalysis] Don't call getTruncateOrZeroExtend for pointers of different sizes (PR #79804)

[Florian Mayer via llvm-commits]

fmayer wrote:

>From the presubmit bot, seems the assertion is not valid:

```
clang: /var/lib/buildkite-agent/builds/linux-56-59b8f5d88-tdgkv-1/llvm-project/github-pull-requests/llvm/lib/Analysis/StackSafetyAnalysis.cpp:283: const SCEV *(anonymous namespace)::StackSafetyLocalAnalysis::getSCEVAsPointer(Value *): Assertion `ValTy->isPointerTy()' failed.
```

https://github.com/llvm/llvm-project/pull/79804