Relax wasi memory export check when wasi-threads is enabled

WebAssembly/wasi-threads#22
WebAssembly/WASI#502

Author: yamt

core/iwasm/interpreter/wasm_loader.c

@@ -4185,7 +4185,20 @@ check_wasi_abi_compatibility(const WASMModule *module,
 
     memory = wasm_loader_find_export(module, "", "memory", EXPORT_KIND_MEMORY,
                                      error_buf, error_buf_size);
-    if (!memory) {
+    if (!memory
+#if WASM_ENABLE_LIB_WASI_THREADS != 0
+        /*
+         * with wasi-threads, it's still an open question if a memory
+         * should be exported.
+         *
+         * https://github.com/WebAssembly/wasi-threads/issues/22
+         * https://github.com/WebAssembly/WASI/issues/502
+         *
+         * Note: this code assumes the number of memories is at most 1.
+         */
+        && module->import_memory_count == 0
+#endif
+    ) {
         set_error_buf(error_buf, error_buf_size,
                       "a module with WASI apis must export memory by default");
         return false;