Avoid errors when converting V128 for the wasm-c-api

For this to work the wasm-c-api must add support for the V128 type (e.g. through __uint128_t)

wasmtime-api/src/wasm.rs

@@ -815,6 +815,7 @@ fn from_valtype(ty: &ValType) -> wasm_valkind_t {
         ValType::F64 => 3,
         ValType::AnyRef => 128,
         ValType::FuncRef => 129,
+        _ => panic!("wasm_valkind_t has no known conversion for {:?}", ty),
     }
 }