re PR libstdc++/52681 ([C++11] Using std::thread without -pthread crashes without warning)

	PR libstdc++/52681
	* src/c++11/thread.cc (thread::_M_start_thread): Improve error text
	when threads are not enabled.

From-SVN: r190330

libstdc++-v3/ChangeLog

+2012-08-12  Jonathan Wakely  <jwakely.gcc@gmail.com>
+
+	PR libstdc++/52681
+	* src/c++11/thread.cc (thread::_M_start_thread): Improve error text
+	when threads are not enabled.
+
 2012-08-09  Jonathan Wakely  <jwakely.gcc@gmail.com>
 
 	* acinclude.m4: Update references to final C++11 standard.

libstdc++-v3/src/c++11/thread.cc

@@ -115,7 +115,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   thread::_M_start_thread(__shared_base_type __b)
   {
     if (!__gthread_active_p())
+#if __EXCEPTIONS
+      throw system_error(make_error_code(errc::operation_not_permitted),
+			 "Enable multithreading to use std::thread");
+#else
       __throw_system_error(int(errc::operation_not_permitted));
+#endif
 
     __b->_M_this_ptr = __b;
     int __e = __gthread_create(&_M_id._M_thread,