[clang-tools-extra] [clang-doc] Refactor error handling to use ExitOnError (PR #141699)

[Paul Kirth via cfe-commits]

================
@@ -49,6 +49,7 @@
 using namespace clang::ast_matchers;
 using namespace clang::tooling;
 using namespace clang;
+static llvm::ExitOnError ExitOnErr;
----------------
ilovepi wrote:

```suggestion

static llvm::ExitOnError ExitOnErr;
```
Nit: newline between using and the declaration

https://github.com/llvm/llvm-project/pull/141699