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

[Aaron Ballman via cfe-commits]

================
@@ -1956,6 +1964,10 @@ class Declarator {
   LLVM_PREFERRED_TYPE(bool)
   unsigned InlineStorageUsed : 1;
 
+  /// Indicates whether this is set as _Export
----------------
AaronBallman wrote:

```suggestion
  /// Indicates whether this is set as _Export.
```

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