[OpenACC] Implement 'tile' attribute AST (#110999)

The 'tile' clause shares quite a bit of the rules with 'collapse', so a
followup patch will add those tests/behaviors. This patch deals with
adding the AST node.

The 'tile' clause takes a series of integer constant expressions, or *.
The asterisk is now represented by a new OpenACCAsteriskSizeExpr node,
else this clause is very similar to others.
diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index 8aedbfc..dbddd6c 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -1593,6 +1593,8 @@
 
   case Stmt::SYCLUniqueStableNameExprClass:
     return CT_Cannot;
+  case Stmt::OpenACCAsteriskSizeExprClass:
+    return CT_Cannot;
   case Stmt::NoStmtClass:
     llvm_unreachable("Invalid class for statement");
   }