Add one more test for optional

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@333252 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/optional/optional.object/optional.object.ctor/deduct.pass.cpp

@@ -41,4 +41,13 @@ int main()
 
 //  Test the implicit deduction guides
 
+    {
+//  optional(const optional &);
+    std::optional<char> source('A');
+    std::optional opt(source);
+    static_assert(std::is_same_v<decltype(opt), std::optional<char>>, "");
+    assert(static_cast<bool>(opt) == static_cast<bool>(source));
+    assert(*opt == *source);
+    }
+
 }