[clang] [SystemZ][z/OS] Add visibility features for z/OS (eg. _Export, pragma export) (PR #111035)

[Aaron Ballman via cfe-commits]

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@@ -7502,6 +7502,27 @@ attribute requires a string literal argument to identify the handle being releas
   }];
 }
 
+def zOSExportDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Use the _Export keyword with a function name or external variable to declare
----------------
AaronBallman wrote:

```suggestion
Use the ``_Export`` keyword on a function or external variable to declare
```

https://github.com/llvm/llvm-project/pull/111035