[clang] Turn `-Wdeprecated-literal-operator` on by default (PR #111027)

[Vlad Serebrennikov via cfe-commits]

================
@@ -99,6 +99,20 @@ C++ Specific Potentially Breaking Changes
     // Was error, now evaluates to false.
     constexpr bool b = f() == g();
 
+- The warning ``-Wdeprecated-literal-operator`` is now on by default, as this is
+  something that WG21 has shown interest in removing from the language. The
+  result is that anyone who is compiling with ``-Werror`` should see this
+  diagnostic.  To fix this diagnostic, simply removing the space character from
+  between the ``operator""`` and the user defined literal name will make the
+  source no longer deprecated. This is consistent with CWG2521.
----------------
Endilll wrote:

```suggestion
  source no longer deprecated. This is consistent with `CWG2521 <https://cplusplus.github.io/CWG/issues/2521.html>_`.
```

https://github.com/llvm/llvm-project/pull/111027