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

[via llvm-commits]

yonghong-song wrote:

Okay, looks like current llvm19/llvm20 already do not have L* labels in symbol table.
@eddyz87 has another pull request (https://github.com/llvm/llvm-project/pull/100550) to address llvm-objdump without-label issue. There are a couple of options to resolve this. Since we do not want L* in the symbol table,
then the only option may be tweak llvm-objdump.

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