Fix bug 19740; round-tripping a pointer through a stream doesn't work

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@209305 91177308-0d34-0410-b5e6-96231b3b80d8

test/input.output/iostream.format/input.streams/istream.formatted/istream.formatted.arithmetic/pointer.pass.cpp

@@ -76,4 +76,22 @@ int main()
         assert(!is.eof());
         assert(!is.fail());
     }
+    {
+        testbuf<char> sb("12345678");
+        std::istream is(&sb);
+        void* n = 0;
+        is >> n;
+        assert(n == (void*)0x12345678);
+        assert( is.eof());
+        assert(!is.fail());
+    }
+    {
+        testbuf<wchar_t> sb(L"12345678");
+        std::wistream is(&sb);
+        void* n = 0;
+        is >> n;
+        assert(n == (void*)0x12345678);
+        assert( is.eof());
+        assert(!is.fail());
+    }
 }