Add a test to make sure we're doing the right thing for throwing exceptions from deferred functions. This is LWG issue #2186. No change to the library needed.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@204678 91177308-0d34-0410-b5e6-96231b3b80d8

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

@@ -55,6 +55,12 @@ std::unique_ptr<int> f4(std::unique_ptr<int>&& p)
     return std::move(p);
 }
 
+void f5(int i)
+{
+    std::this_thread::sleep_for(ms(200));
+    throw i;
+}
+
 int main()
 {
     {
@@ -174,4 +180,17 @@ int main()
         Clock::time_point t1 = Clock::now();
         assert(t1-t0 < ms(100));
     }
+
+    {
+        std::future<void> f = std::async(f5, 3);
+        std::this_thread::sleep_for(ms(300));
+        try { f.get(); assert (false); } catch ( int ex ) {}
+    }
+
+    {
+        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 ) {}
+    }
+
 }