[patch] Fix two small issues

[Jonathan Wakely]

The first change works around a compiler error in <mutex> in c++1y
mode, I think it's a front end bug (reported as PR 57573) but is easy
to solve with this change.

The second changes a test to avoid calling try_lock() when the calling
thread already owns the mutex, but moving the try_lock() call into a
new thread.

        * include/std/mutex (call_once): Remove parentheses to fix error in
        c++1y and gnu++1y mode.
        * testsuite/30_threads/mutex/try_lock/2.cc: Call try_lock() in new
        thread to avoid undefined behaviour.

Tested x86_64-linux, committed to trunk.

commit a548855f6c161971cd34b973dc9dc3c5b5663112
Author: Jonathan Wakely <jwakely....@gmail.com>
Date:   Sun Jun 9 16:54:20 2013 +0100

        * include/std/mutex (call_once): Remove parentheses to fix error in
        c++1y and gnu++1y mode.
        * testsuite/30_threads/mutex/try_lock/2.cc: Call try_lock() in new
        thread to avoid undefined behaviour.

diff --git a/libstdc++-v3/include/std/mutex b/libstdc++-v3/include/std/mutex
index 3c666c1..cdd05a3 100644
--- a/libstdc++-v3/include/std/mutex
+++ b/libstdc++-v3/include/std/mutex
@@ -783,7 +783,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __set_once_functor_lock_ptr(&__functor_lock);
 #endif
 
-      int __e = __gthread_once(&(__once._M_once), &__once_proxy);
+      int __e = __gthread_once(&__once._M_once, &__once_proxy);
 
 #ifndef _GLIBCXX_HAVE_TLS
       if (__functor_lock)
diff --git a/libstdc++-v3/testsuite/30_threads/mutex/try_lock/2.cc 
b/libstdc++-v3/testsuite/30_threads/mutex/try_lock/2.cc
index bb3fcd4..f2a6723 100644
--- a/libstdc++-v3/testsuite/30_threads/mutex/try_lock/2.cc
+++ b/libstdc++-v3/testsuite/30_threads/mutex/try_lock/2.cc
@@ -24,6 +24,7 @@
 
 
 #include <mutex>
+#include <thread>
 #include <system_error>
 #include <testsuite_hooks.h>
 
@@ -38,15 +39,18 @@ int main()
       m.lock();
       bool b;
 
-      try
-       {
-         b = m.try_lock();
-         VERIFY( !b );
-       }
-      catch (const std::system_error& e)
-       {
-         VERIFY( false );
-       }
+      std::thread t([&] {
+        try
+          {
+            b = m.try_lock();
+          }
+        catch (const std::system_error& e)
+          {
+            VERIFY( false );
+          }
+      });
+      t.join();
+      VERIFY( !b );
 
       m.unlock();
     }