Fix race conditions in test class used throughout the std::thread tests.

The test class 'G' reads and writes to the same static variables in its
constructor, destructor and call operator. When threads are
constructed using `std::thread t((G()))` there is a race condition between the
destruction of the temporary and the execution of `G::operator()()`.

The fix is to simply create the input before creating the thread.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@233946 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/thread/thread.threads/thread.thread.class/thread.thread.assign/move.pass.cpp

@@ -48,13 +48,16 @@ int main()
     {
         assert(G::n_alive == 0);
         assert(!G::op_run);
-        std::thread t0(G(), 5, 5.5);
+        {
+        G g;
+        std::thread t0(g, 5, 5.5);
         std::thread::id id = t0.get_id();
         std::thread t1;
         t1 = std::move(t0);
         assert(t1.get_id() == id);
         assert(t0.get_id() == std::thread::id());
         t1.join();
+        }
         assert(G::n_alive == 0);
         assert(G::op_run);
     }