[clang] docs(clang): add some missing flags (PR #209519)

[Balázs Benics via cfe-commits]

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@@ -349,6 +349,28 @@ output format of the diagnostics that it generates.
        ::
 
            t.c +3:11: warning: conversion specifies type 'char *' but the argument has type 'int'
+
+   **sarif**
+       Emit diagnostics as a `SARIF <https://sarifweb.azurewebsites.net/>`_ JSON document.
+       This is useful when diagnostics are consumed by tools, including AI agents.
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steakhal wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/209519