Implement post-MVP features and native stack overflow check (#243)

Implement native thread stack overflow check
Implement post-MVP: Non-trapping float-to-int conversions
Implement post-MVP: Sign-extension operators
Enhance WASM loader checks

core/shared/platform/linux-sgx/sgx_thread.c

@@ -47,3 +47,9 @@ int os_cond_destroy(korp_cond *cond)
     return BHT_OK;
 }
 
+uint8 *os_thread_get_stack_boundary()
+{
+    /* TODO: get sgx stack boundary */
+    return NULL;
+}
+