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

[Aaron Ballman via cfe-commits]

================
@@ -2110,6 +2126,18 @@ class Declarator {
       Range.setEnd(SR.getEnd());
   }
 
+  /// Set this declarator as _Export
----------------
AaronBallman wrote:

```suggestion
  /// Set this declarator as _Export.
```
I'll stop commenting on these now, can you take a pass over all the new comments you've added and ensure they have appropriate trailing punctuation?

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