[llvm] [Transforms] Introduce BuildBuiltins.h atomic helpers (PR #134455)

[James Y Knight via llvm-commits]

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@@ -222,6 +264,13 @@ detail::ValueMatchesPoly<M> HasValue(M Matcher) {
   return detail::ValueMatchesPoly<M>(Matcher);
 }
 
+/// Matches on Expected<T> values that succeed, but also stores its value into a
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jyknight wrote:

Maybe this addition to the testing support should go in a different PR?

https://github.com/llvm/llvm-project/pull/134455