[llvm] [MC] Replace fragment ilist with singly-linked lists (PR #95077)

[via llvm-commits]

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@@ -107,6 +115,11 @@ class MCSection {
   };
   SmallVector<PendingLabel, 2> PendingLabels;
 
+  // Mapping from subsection number to fragment list. At layout time, the
+  // subsection 0 list is replaced with concatenated fragments from all
+  // subsections.
+  SmallVector<std::pair<unsigned, std::unique_ptr<FragList>>, 1> Subsections;
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aengelke wrote:

Why a unique_ptr? Whenever Subsections is updated, also CurFragList is updated, so no dangling pointer could occur?

https://github.com/llvm/llvm-project/pull/95077