[libcxx] [test] Replace one more occurrence of non-Standard std::launch::any with AnyPolicy.

[STL_MSFT]

Summary

[libcxx] [test] Replace one more occurrence of non-Standard std::launch::any with AnyPolicy.

Also, fix MSVC "warning C4101: 'ex': unreferenced local variable".

[EricWF]

Woops, guess I was a bit careless there.

[EricWF]

r268153.

test/std/thread/futures/futures.async/async.pass.cpp

LIBCPP_ASSERT(AnyPolicy == std::launch::any);
         test<int&>(checkIntRef, true,  std::launch::deferred, f1);
         test<int&>(checkIntRef, DPID,  AnyPolicy, f1);
     }
     {
         auto checkVoid = [](std::future<void>& f) { f.get(); return true; };
         test<void>(checkVoid, DPID,  f2);
         test<void>(checkVoid, false, std::launch::async, f2);
         test<void>(checkVoid, true,  std::launch::deferred, f2);
-        test<void>(checkVoid, DPID,  std::launch::any, f2);
+        test<void>(checkVoid, DPID,  AnyPolicy, f2);
     }
     {
         using Ret = std::unique_ptr<int>;
         auto checkUPtr = [](std::future<Ret>& f) { return *f.get() == 3; };
         test<Ret>(checkUPtr, DPID, f3, 3);
         test<Ret>(checkUPtr, DPID, f4, std::unique_ptr<int>(new int(3)));
     }
     {
         std::future<void> f = std::async(f5, 3);
         std::this_thread::sleep_for(ms(300));
-        try { f.get(); assert (false); } catch ( int ex ) {}
+        try { f.get(); assert (false); } catch ( int ) {}
     }
     {
         std::future<void> f = std::async(std::launch::deferred, f5, 3);
         std::this_thread::sleep_for(ms(300));
-        try { f.get(); assert (false); } catch ( int ex ) {}
+        try { f.get(); assert (false); } catch ( int ) {}
     }
 }