We can't (don't want to) honor the same set of "-fuse-ld" flags
with WebAssembly since the ELF linkers (ld.lld, ld.gnu, etc) don't
work with wasm object files.
Instead we implement our own linker finding logic, similar or other
non-ELF platforms like MSVC.
We've had a few issues with CLANG_DEFAULT_LINKER overriding the
WebAssembly linker which doesn't make sense since there is no generic
linker that can handle WebAssembly today.
I'd also consider handling the else if (UseLinker.empty() || UseLinker == "ld") case which should return the default linker (i.e. wasm-ld), this matches the behavior of the generic driver logic in ToolChain and can be used to select the default linker for the target.