[llvm] [LoopInterchange] Add loop names to debug messages. NFC (PR #172855)

[Michael Kruse via llvm-commits]

================
@@ -642,8 +642,14 @@ struct LoopInterchange {
 
     unsigned LoopNestDepth = LoopList.size();
 
-    LLVM_DEBUG(dbgs() << "Processing LoopList of size = " << LoopNestDepth
-                      << "\n");
+    LLVM_DEBUG(
----------------
Meinersbur wrote:

You can also have multiple lines in `LLVM_DEBUG`, e.g.
https://github.com/llvm/llvm-project/blob/main/clang/include/clang/Analysis/FlowSensitive/StorageLocation.h#L128-L138

Or use
```c++
#include <llvm/Support/DebugLog.h>
LDBG() <<  "Processing LoopList of size = " << LoopNestDepth << "\n";
```

https://github.com/llvm/llvm-project/pull/172855