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

[via llvm-commits]

yonghong-song wrote:

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

Thanks, @eddyz87 I added additional checking for line_num == 0. Now I checked with bpf selftest and our internal bpf program, there is zero line info with line_num == 0. But please double check.

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