C11 threads: Move implementation to sysdeps/pthread

so it gets shared by nptl and htl. Also add htl versions of thrd_current and
thrd_yield.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

sysdeps/pthread/thrd_priv.h

@@ -0,0 +1,45 @@
+/* Internal C11 threads definitions.
+   Copyright (C) 2018-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef THRD_PRIV_H
+# define THRD_PRIV_H
+
+#include <features.h>
+#include <threads.h>
+#include <errno.h>
+#include "pthreadP.h"	/* For pthread_{mutex,cond}_t definitions.  */
+
+static __always_inline int
+thrd_err_map (int err_code)
+{
+  switch (err_code)
+  {
+    case 0:
+      return thrd_success;
+    case ENOMEM:
+      return thrd_nomem;
+    case ETIMEDOUT:
+      return thrd_timedout;
+    case EBUSY:
+      return thrd_busy;
+    default:
+      return thrd_error;
+  }
+}
+
+#endif