pthread: Introduce __pthread_early_init

This function is called from __libc_early_init to initialize the
pthread subsystem.

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

sysdeps/pthread/pthread_early_init.h

@@ -0,0 +1,29 @@
+/* pthread initialization called from __libc_early_init.  Generic version.
+   Copyright (C) 2021 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 _PTHREAD_EARLY_INIT_H
+#define _PTHREAD_EARLY_INIT_H 1
+
+static inline void
+__pthread_early_init (void)
+{
+  /* The generic version does not require any additional
+     initialization.  */
+}
+
+#endif  /* _PTHREAD_EARLY_INIT_H */