[llvm] [LV] Improve code using [[maybe_unused]] (NFC) (PR #137138)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

RFC for deprecating void casts: https://discourse.llvm.org/t/coding-standard-deprecate-use-of-void-cast-to-suppress-unused-variable-warnings/86705/18.

https://github.com/llvm/llvm-project/pull/137138