[llvm] [LLVM][DebugInfo]Allow ExtraData field to be a node reference (PR #165023)

[Laxman Sole via llvm-commits]

laxmansole wrote:

>I am unfamiliar with numba-cuda, can you explain how the metadata node references will be used? An example could be useful

Let’s consider the following two cases. Both are valid LLVM IR examples; however, the second case triggers an assertion because the backend lacks proper handling (which this PR addresses).

```
!20 = !DIDerivedType(tag: DW_TAG_member, name: "const_val", scope: !18, file: !1, line: 11, baseType: !21, flags: DIFlagStaticMember, extraData: i32 42)
```

```
!22 = !{i32 42} ; Static member constant value
!20 = !DIDerivedType(tag: DW_TAG_member, name: "const_val", scope: !18, file: !1, line: 11, baseType: !21, flags: DIFlagStaticMember, extraData: !22)
```

`llvmlite` was previously unable to emit the first form due to certain limitations, but this issue has been resolved recently -https://github.com/numba/llvmlite/pull/1326. 

https://github.com/llvm/llvm-project/pull/165023