toywasm_repl_invoke: wait for other threads in case of non-trap return

Note: for some reasons, the current logic in wasi-libc crt returns
without wasi_proc_exit when the exit code is 0.  maybe just to save
a host call?

cf. WebAssembly/wasi-libc#367

cli/repl.c

@@ -819,6 +819,12 @@ toywasm_repl_invoke(struct repl_state *state, const char *modname,
                         goto fail;
                 }
                 print_trap(ctx, trap);
+        } else {
+#if defined(TOYWASM_ENABLE_WASI_THREADS)
+                if (state->wasi_threads != NULL) {
+                        wasi_threads_instance_join(state->wasi_threads);
+                }
+#endif
         }
         exec_context_clear(ctx);
         if (ret != 0) {