[libunwind] Silence -Wunused-parameter warnings in Unwind-wasm.c (PR #125412)

[Sam Clegg via cfe-commits]

sbc100 wrote:

It seems that libunwind builds with C++17: https://github.com/llvm/llvm-project/blob/3bf53844cfedf09f22d2786e57ef81d5d41fe249/libunwind/src/CMakeLists.txt#L139-L145

Which means this change actually breaks the build.  We were about to bump to C++23 downstream but that seems like the wrong solution if upstream is on C++17: https://github.com/emscripten-core/emscripten/pull/26037#discussion_r2686805303

If this analysis is correct then I propose this change is reverted, and that the revert is backported to LLVM 21.

https://github.com/llvm/llvm-project/pull/125412