[lld] [llvm] [MC] Rename temporary symbols of empty name to ".L0" (PR #89693)

[James Henderson via llvm-commits]

https://github.com/jh7370 approved this pull request.

"Fixes" link to the issue?

LGTM in principle, but might want another review from someone with a little more knowledge of e.g. RISC-V.

https://github.com/llvm/llvm-project/pull/89693