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

[Jeremy Morse via llvm-commits]

jmorse wrote:

Thanks for the IR sample on D159485 -- I think this is certainly a legitimate use of IRBuilder even if we're trying to diminish and eliminate debug intrinsics [0]. The unit test in #66491 looks good too -- combine that with the style fix and we're good to go!

[0] Coming soon to a compiler near you soon!

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