[llvm] [WebAssembly] Guard use of getSymbolName with isSymbol (PR #156105)

[via llvm-commits]

https://github.com/QuantumSegfault commented:

This fix works for me.

I considered opening a PR myself, but wasn't sure the problem/fix was as simple as it seemed (and is).

https://github.com/llvm/llvm-project/pull/156105