[llvm] [ADT] Deprecate PointerUnion::{is,get} (NFC) (PR #122623)

[Kazu Hirata via llvm-commits]

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@@ -147,12 +147,18 @@ class PointerUnion
   //        isa<T>, cast<T> and the llvm::dyn_cast<T>
 
   /// Test if the Union currently holds the type matching T.
-  template <typename T> inline bool is() const { return isa<T>(*this); }
+  template <typename T>
+  LLVM_DEPRECATED("Use isa instead", "isa")
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kazutakahirata wrote:

OK.  I've switched to `[[deprecated(MSG)]]` for this PR.  Thanks!

https://github.com/llvm/llvm-project/pull/122623