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

[via llvm-commits]

eddyz87 wrote:

> Looks good, I'll double check the impact on line information in selftests and write back this evening.

I used the following (ugly) [script](https://gist.github.com/eddyz87/807e7c3b8707ae042c0fcccfe6f09938) to dump all line information for *.bpf.o files generated for kernel selftests. It appears that there is no difference between line information generated for this branch and for 'main'.

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