Implement pthread_cond_broadcast wrapper for lib-pthread (#982)

Implement pthread_cond_broadcast wrapper for lib-pthread
- support pthread_cond_broadcast wrapper for posix/linux-sgx/windows
- update document for building multi-thread wasm app with emcc

core/shared/platform/common/posix/posix_thread.c

@@ -262,6 +262,17 @@ os_cond_signal(korp_cond *cond)
     return BHT_OK;
 }
 
+int
+os_cond_broadcast(korp_cond *cond)
+{
+    assert(cond);
+
+    if (pthread_cond_broadcast(cond) != BHT_OK)
+        return BHT_ERROR;
+
+    return BHT_OK;
+}
+
 int
 os_thread_join(korp_tid thread, void **value_ptr)
 {

core/shared/platform/include/platform_api_extension.h

@@ -179,6 +179,16 @@ os_cond_reltimedwait(korp_cond *cond, korp_mutex *mutex, uint64 useconds);
 int
 os_cond_signal(korp_cond *cond);
 
+/**
+ * Broadcast the condition variable
+ *
+ * @param cond condition variable
+ *
+ * @return 0 if success
+ */
+int
+os_cond_broadcast(korp_cond *cond);
+
 /****************************************************
  *                     Section 2                    *
  *                   Socket support                 *

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

@@ -164,6 +164,19 @@ os_cond_signal(korp_cond *cond)
     return BHT_OK;
 }
 
+int
+os_cond_broadcast(korp_cond *cond)
+{
+#ifndef SGX_DISABLE_PTHREAD
+    assert(cond);
+
+    if (pthread_cond_broadcast(cond) != BHT_OK)
+        return BHT_ERROR;
+
+#endif
+    return BHT_OK;
+}
+
 int
 os_thread_join(korp_tid thread, void **value_ptr)
 {

core/shared/platform/windows/win_thread.c

@@ -567,6 +567,24 @@ os_cond_signal(korp_cond *cond)
     return BHT_OK;
 }
 
+int
+os_cond_broadcast(korp_cond *cond)
+{
+    /* Signal all of the wait node of wait list */
+    os_mutex_lock(&cond->wait_list_lock);
+    if (cond->thread_wait_list) {
+        os_thread_wait_node *p = cond->thread_wait_list;
+        while (p) {
+            os_sem_signal(&p->sem);
+            p = p->next;
+        }
+    }
+
+    os_mutex_unlock(&cond->wait_list_lock);
+
+    return BHT_OK;
+}
+
 static os_thread_local_attribute uint8 *thread_stack_boundary = NULL;
 
 static ULONG