[flang] [llvm] [flang][Parser][OpenMP] Fix unparser for cancellation_construct_type (PR #136001)

[Krzysztof Parzyszek via llvm-commits]

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@@ -83,6 +83,9 @@ class Clause<string c> {
   // Optional class holding value of the clause in flang AST.
   string flangClass = "";
 
+  // If set to true, don't emit flang Unparser.
+  bit skipFlangUnparser = false;
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kparzysz wrote:

Could you rename this to `isArtificial`?  There may be more future cases for this, and more places to check this flag.

https://github.com/llvm/llvm-project/pull/136001