Add thread support

include/bh/internal/thread_posix.h

@@ -0,0 +1,30 @@
+#include <pthread.h>
+
+struct bh_thread_s
+{
+    pthread_t handle;
+};
+
+struct bh_mutex_s
+{
+    pthread_mutex_t handle;
+};
+
+struct bh_cond_s
+{
+    pthread_cond_t handle;
+};
+
+int bh_thread_init(bh_thread_t *thread,
+                   bh_task_t *task);
+
+int bh_mutex_init(bh_mutex_t *mutex);
+void bh_mutex_destroy(bh_mutex_t *mutex);
+
+int bh_cond_init(bh_cond_t *cond);
+void bh_cond_destroy(bh_cond_t *cond);
+
+int bh_thread_pool_init(bh_thread_pool_t *pool,
+                        size_t size);
+
+void bh_thread_pool_destroy(bh_thread_pool_t *pool);