[llvm] [BPF] Use ".L" local prefix label for basic blocks (PR #95103)

[via llvm-commits]

4ast wrote:

> Just want to confirm. @4ast You perfer to use prefix 'L' for all temp labels?

Yes. As this patch implements it. The issue we had is that those L labels were in symbol table. This patch is fixing that.

https://github.com/llvm/llvm-project/pull/95103