[atomics.flag] completed. Initialization is not working on clang and can't be made to work without defaulted default constructors.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@115207 91177308-0d34-0410-b5e6-96231b3b80d8

test/atomics/atomics.flag/copy_assign.fail.cpp

@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <atomic>
+
+// struct atomic_flag
+
+// atomic_flag& operator=(const atomic_flag&) = delete;
+
+#include <atomic>
+#include <cassert>
+
+int main()
+{
+    std::atomic_flag f0;
+    std::atomic_flag f;
+    f = f0;
+}