[llvm] [LLVM] Fix a bug in `Intrinsic::getFnAttributes` (PR #161248)

[Nikita Popov via llvm-commits]

https://github.com/nikic approved this pull request.

LGTM. Alternatively we could make the "no fn attrs" case less special by getIntrinsicFnAttributeSet() handle that by returning an empty attribute set -- but we'd probably still want an explicit check in getAttributes() to avoid pushing the FunctionIndex, so maybe that's not worthwhile.

https://github.com/llvm/llvm-project/pull/161248