[llvm] BPF: Use DebugLoc to find Filename for BTF line info (PR #90302)

[via llvm-commits]

eddyz87 wrote:

@yonghong-song, I've updated the [script](https://gist.github.com/eddyz87/807e7c3b8707ae042c0fcccfe6f09938) to use `llvm-objdump` binary to extract BTF/BTF.ext section contents. I've also switched to using your branch `dev2` instead of `dev`. After these changes I do see some changes in new vs old generated line info, it could be summarized as followos:
- line info with line 0 is not generated anymore;
- this causes removal of a few (~400) line infos in cases like below:

```diff
Insn       File                 Line Col
...
 1968       bpf_cubic.c          359  17  		delta = (cwnd * scale) >> 3;
 1984       bpf_cubic.c          360  27  		if (ca->ack_cnt > delta && delta) {
-1992       bpf_cubic.c          0    0   (anon)
-2008       bpf_cubic.c          360  27  		if (ca->ack_cnt > delta && delta) {
```

The record for instruction 2008 is removed, because it's coordinate is identical to record for instruction 1984.

=> I think that it is safe to merge this patch.

https://github.com/llvm/llvm-project/pull/90302