[DebugInfo] Fix memory leak in DebugSSAUpdater

Fixes an issue in commit 3946c50, PR llvm#135349.

The DebugSSAUpdater class performs raw pointer allocations. It frees these
properly in reset(), but does not do so in its destructor - as an immediate
fix, this patch adds a destructor which frees the allocations correctly.

Author: SLTozer

llvm/include/llvm/Transforms/Utils/DebugSSAUpdater.h

@@ -235,6 +235,11 @@ class DebugSSAUpdater {
   DebugSSAUpdater(const DebugSSAUpdater &) = delete;
   DebugSSAUpdater &operator=(const DebugSSAUpdater &) = delete;
 
+  ~DebugSSAUpdater() {
+    for (auto &Block : BlockMap)
+      delete Block.second;
+  }
+
   void reset() {
     for (auto &Block : BlockMap)
       delete Block.second;