[clang] [clang] Factor out OpenACC part of `Sema` (PR #84184)

[Erich Keane via cfe-commits]

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@@ -1162,6 +1162,11 @@ class Sema final {
   /// CurContext - This is the current declaration context of parsing.
   DeclContext *CurContext;
 
+  SemaOpenACC &OpenACC() {
+    assert(OpenACCPtr);
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erichkeane wrote:

IMO, there is value to having the assert.  I can definitely see a world where the sub-types are allowed to get 'big enough' that restricting them to only be created 'sometimes' has value.  

https://github.com/llvm/llvm-project/pull/84184