[llvm] [Support] Move UndefPoisonKind enum to a shared header (PR #195523)

[Nikita Popov via llvm-commits]

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@@ -23,6 +23,7 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/UndefPoison.h"
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nikic wrote:

Why is this included in the header rather than the source file?

https://github.com/llvm/llvm-project/pull/195523