Support: Add closing namespace comment in raw_ostream_test.cpp, NFC

The closing namespace comment prevents clang-format from dropping a
blank line after the final test. Also add in a blank line (which
simplifies merging/rebasing/etc. WIP patches).

llvm/unittests/Support/raw_ostream_test.cpp

@@ -543,4 +543,5 @@ TEST(raw_ostreamTest, writeToStdOut) {
   std::string CapturedStdOut = testing::internal::GetCapturedStdout();
   EXPECT_EQ(CapturedStdOut, "HelloWorld");
 }
-}
+
+} // namespace