Fix execute_main not wait for other threads (#1137)

Fix wasm_application_execute_main/wasm_application_execute_func not waiting for
other threads to terminate in multi-thread mode, which causes that the exception
thrown by other threads may haven't been spreaded to current main thread, and
cannot be detected by the caller, as reported in #1131.

core/iwasm/common/wasm_exec_env.h

@@ -100,6 +100,9 @@ typedef struct WASMExecEnv {
     korp_cond wait_cond;
     /* the count of threads which are joining current thread */
     uint32 wait_count;
+
+    /* whether current thread is detached */
+    bool thread_is_detached;
 #endif
 
 #if WASM_ENABLE_DEBUG_INTERP != 0