[llvm] [DebugInfo] Add clang flag to enable function-level debug line attribution (PR #93985)

[via llvm-commits]

alx32 wrote:

@dwblaikie
> So it's only possible to refer to the very start of the line table in this way

Oh I see. Would it be possible to specify it as a numeric offset (at least for the purpose of this change) ? i.e:
```
 .long  0x41   # DW_AT_META_stmt_sequence
```

https://github.com/llvm/llvm-project/pull/93985