[llvm] [MC] Make ELFUniquingMap a StringMap (PR #95006)

[Fangrui Song via llvm-commits]

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@@ -350,7 +325,7 @@ class MCContext {
   };
 
   StringMap<MCSectionMachO *> MachOUniquingMap;
-  std::map<ELFSectionKey, MCSectionELF *> ELFUniquingMap;
+  StringMap<MCSectionELF *> ELFUniquingMap;
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MaskRay wrote:

Move ELF after COFF to move to a lexicographical order... (MachO is an outlier)

https://github.com/llvm/llvm-project/pull/95006