[llvm] Instruction: avoid crash in getStableDebugLoc when `this` isn't a DbgInfoIntrinsic (PR #66266)

[Augie Fackler via llvm-commits]

durin42 wrote:

The windows ninja failure is at a high enough level I suspect it's misconfiguration and is wholly unrelated to this change.

https://github.com/llvm/llvm-project/pull/66266