[llvm] change contents of ScalarEvolution from private to protected (PR #83052)

[Joshua Ferguson via llvm-commits]

https://github.com/skewballfox created https://github.com/llvm/llvm-project/pull/83052

hi, new to contributing to LLVM. Necessary to resolve [Enzyme#1607](https://github.com/EnzymeAD/Enzyme/issues/1607). Enzyme inherits from ScalarEvolution and was previously relying on `#define private public` to make this work. 

I ran this through clang format, and compiled both locally, if there is more test I need to run prior to pushing commits to PRs in the future, please let me know

>From eea887cf6be39856fa441ed48f72c1c9177a76a6 Mon Sep 17 00:00:00 2001
From: Joshua Ferguson <joshua.ferguson.273 at gmail.com>
Date: Sun, 25 Feb 2024 14:06:02 -0600
Subject: [PATCH] mainly pushing to switch machines

---
 llvm/include/llvm/Analysis/ScalarEvolution.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 0880f9c65aa45d..1b03437de30c28 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1345,7 +1345,7 @@ class ScalarEvolution {
     }
   };
 
-private:
+protected:
   /// A CallbackVH to arrange for ScalarEvolution to be notified whenever a
   /// Value is deleted.
   class SCEVCallbackVH final : public CallbackVH {