[clang] [OpenACC] Implement Atomic construct variants (PR #73015)

[Alexey Bataev via cfe-commits]

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@@ -94,6 +94,37 @@ void func() {
 #pragma acc kernels loop
   for(;;){}
 
+  int i = 0, j = 0, k = 0;
+  // expected-error at +2{{missing OpenACC 'atomic-clause'; expected 'read', 'write', 'update', or 'capture'}}
+  // expected-warning at +1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc atomic
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alexey-bataev wrote:

It is allowed by the standard, means same as atomic update

https://github.com/llvm/llvm-project/pull/73015