[patch] libstdc++/70503 Ensure std::thread helpers have internal linkage

[Jonathan Wakely <jwakely at redhat dot com>]

This makes the execute_native_thread_routine* helpers 'static' rather
than using an unnamed namespace, because the latter doesn't give them
static linkage due to them being extern "C".

Tested x86_64-linux, committed to trunk. Backports to gcc-5 and
gcc-4.9 to follow soon.

commit 84538059d9d8608c550e11627b28c5ff34fb2edd
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Apr 5 14:17:57 2016 +0100

    Ensure std::thread helpers have internal linkage
    
    	PR libstdc++/70503
    	* src/c++11/thread.cc (execute_native_thread_routine,
    	execute_native_thread_routine_compat): Give internal linkage.
    	* testsuite/30_threads/thread/70503.cc: New test.

diff --git a/libstdc++-v3/src/c++11/thread.cc b/libstdc++-v3/src/c++11/thread.cc
index d2a7dc3..a027fcf 100644
--- a/libstdc++-v3/src/c++11/thread.cc
+++ b/libstdc++-v3/src/c++11/thread.cc
@@ -71,9 +71,9 @@ static inline int get_nprocs()
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
-  namespace
+  extern "C"
   {
-    extern "C" void*
+    static void*
     execute_native_thread_routine(void* __p)
     {
       thread::_State_ptr __t{ static_cast<thread::_State*>(__p) };
@@ -95,7 +95,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
     }
 
 #if _GLIBCXX_THREAD_ABI_COMPAT
-    extern "C" void*
+    static void*
     execute_native_thread_routine_compat(void* __p)
     {
       thread::_Impl_base* __t = static_cast<thread::_Impl_base*>(__p);
@@ -121,7 +121,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
       return nullptr;
     }
 #endif
-  }
+  } // extern "C"
 
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
diff --git a/libstdc++-v3/testsuite/30_threads/thread/70503.cc b/libstdc++-v3/testsuite/30_threads/thread/70503.cc
new file mode 100644
index 0000000..1763ac2
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/thread/70503.cc
@@ -0,0 +1,33 @@
+// Copyright (C) 2016 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 link }
+// { dg-options " -std=gnu++11 -static" { target *-*-*gnu* } }
+// { dg-require-cstdint "" }
+// { dg-require-gthreads "" }
+
+extern "C" {
+  void execute_native_thread_routine(void);
+  void execute_native_thread_routine_compat(void);
+}
+
+int main()
+{
+  execute_native_thread_routine(); // { dg-error "undefined reference" }
+  execute_native_thread_routine_compat(); // { dg-error "undefined reference" }
+}
+// { dg-prune-output "collect2: error: ld returned" }