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

[Aaron Ballman via cfe-commits]

================
@@ -4456,6 +4456,12 @@ void Parser::ParseDeclarationSpecifiers(
       isInvalid = DS.setFunctionSpecNoreturn(Loc, PrevSpec, DiagID);
       break;
 
+    case tok::kw__Export:
+      // If we find kw__Export, it is being applied to a var or function
+      // This will be handled in ParseDeclaratorInternal()
----------------
AaronBallman wrote:

> in int _Export x,y; only x is exported.

That is deeply strange behavior IMO. I can't think of anything else in the language that works like that in that syntactic position.

> We do have to match the existing XL compiler for backwards compatibility.

That can be handled in the downstream too. For example, in this case, I would expect a diagnostic to let the user know that `_Export` very likely does not behave the way they expect in your code example.


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