Non-SFI mode: Use clone() instead of pthread_create()

src/nonsfi/linux/linux_pthread_private.h

+/*
+ * Copyright 2015 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef NATIVE_CLIENT_SRC_NONSFI_LINUX_LINUX_PTHREAD_PRIVATE_H_
+#define NATIVE_CLIENT_SRC_NONSFI_LINUX_LINUX_PTHREAD_PRIVATE_H_ 1
+
+#include "native_client/src/include/nacl_base.h"
+
+EXTERN_C_BEGIN
+
+/*
+ * Creates a new thread by calling clone(). This function does use the |stack|
+ * parameter and the thread's entrypoint is |start_func| with |thread_ptr| as
+ * its parameter.
+ */
+int nacl_user_thread_create(void *(*start_func)(void *), void *stack,
+                            void *thread_ptr);
+
+/*
+ * Exits a thread started by |nacl_user_thread_create|. Threads started with
+ * pthread_create() should terminate by calling pthread_exit() instead.
+ */
+void nacl_user_thread_exit(int32_t *stack_flag);
+
+EXTERN_C_END
+
+#endif