[llvm] [BOLT][DWARF] Refactor legacy ranges writers (PR #96006)

[Maksim Panchenko via llvm-commits]

================
@@ -89,6 +89,15 @@ class DWARFRewriter {
   /// Store Rangelists writer for each DWO CU.
   RangeListsDWOWriers RangeListsWritersByCU;
 
+  /// Contains ranges writer and die.
+  struct RangesWriterAndDIE {
+    std::unique_ptr<DebugRangesSectionWriter> Writer;
+    DIE *Die;
----------------
maksfb wrote:

If we expect these two to be tied together, maybe make `Die` an optional field in `DebugRangesSectionWriter`?

https://github.com/llvm/llvm-project/pull/96006