[clang] [Clang] Warn on backslash-newline-EOF (PR #97585)

[Vlad Serebrennikov via cfe-commits]

================
@@ -536,3 +536,12 @@ namespace cwg1696 { // cwg1696: 7
   };
 #endif
 }
+
+// cwg1698: yes
----------------
Endilll wrote:

```suggestion
// cwg1698: 2.7
```

https://github.com/llvm/llvm-project/pull/97585