[clang] [clang][bytecode][NFC] Make string pointer check more explicit (PR #233360)

[Chen Miao via cfe-commits]

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@@ -1024,7 +1024,7 @@ bool CheckLoad(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
   }
 
   // Block and string pointers are the only ones we can actually read from.
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ChenMiaoi wrote:

Should we update the comment as well? Block pointers have already been handled above, so this check now only concerns string pointers.

https://github.com/llvm/llvm-project/pull/233360