libstdc++: Fix call to __glibcxx_rwlock_init (PR 93244)

When the target doesn't define PTHREAD_RWLOCK_INITIALIZER we use a
wrapper around pthread_wrlock_init, but the wrapper only takes one
argument and we try to call it with two.

This went unnnoticed on most targets because they do define the
PTHREAD_RWLOCK_INITIALIZER macro, but it causes a bootstrap failure on
darwin8.

	PR libstdc++/93244
	* include/std/shared_mutex [!PTHREAD_RWLOCK_INITIALIZER]
	(__shared_mutex_pthread::__shared_mutex_pthread()): Remove incorrect
	second argument to __glibcxx_rwlock_init.
	* testsuite/30_threads/shared_timed_mutex/94069.cc: New test.

libstdc++-v3/ChangeLog

 2020-03-06  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/93244
+	* include/std/shared_mutex [!PTHREAD_RWLOCK_INITIALIZER]
+	(__shared_mutex_pthread::__shared_mutex_pthread()): Remove incorrect
+	second argument to __glibcxx_rwlock_init.
+	* testsuite/30_threads/shared_timed_mutex/94069.cc: New test.
+
+	PR libstdc++/93244
 	* testsuite/27_io/filesystem/path/generic/generic_string.cc: Adjust
 	test to not fail due to PR 94063.
 	* testsuite/27_io/filesystem/path/generic/utf.cc: Likewise.

libstdc++-v3/include/std/shared_mutex

@@ -160,7 +160,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   public:
     __shared_mutex_pthread()
     {
-      int __ret = __glibcxx_rwlock_init(&_M_rwlock, NULL);
+      int __ret = __glibcxx_rwlock_init(&_M_rwlock);
       if (__ret == ENOMEM)
 	__throw_bad_alloc();
       else if (__ret == EAGAIN)

libstdc++-v3/testsuite/30_threads/shared_timed_mutex/94069.cc

+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This 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 General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do compile }
+// { dg-options "-pthread"  }
+// { dg-require-effective-target c++14 }
+// { dg-require-effective-target pthread }
+// { dg-require-gthreads "" }
+//
+#include <pthread.h>
+// This is probably undefined, but we do it to simulate a Pthreads target
+// that doesn't define the macro:
+#undef PTHREAD_RWLOCK_INITIALIZER
+#include <shared_mutex>