Fix build with libcxx22
https://github.com/llvm/llvm-project/pull/160804

Index: llvm/lib/Target/Hexagon/RDFCopy.cpp
--- llvm/lib/Target/Hexagon/RDFCopy.cpp.orig
+++ llvm/lib/Target/Hexagon/RDFCopy.cpp
@@ -108,7 +108,7 @@ bool CopyPropagation::scanBlock(MachineBasicBlock *B) 
   for (NodeAddr<InstrNode*> IA : BA.Addr->members(DFG)) {
     if (DFG.IsCode<NodeAttrs::Stmt>(IA)) {
       NodeAddr<StmtNode*> SA = IA;
-      EqualityMap EM(std::less<RegisterRef>(DFG.getPRI()));
+      EqualityMap EM(RegisterRefLess(DFG.getPRI()));
       if (interpretAsCopy(SA.Addr->getCode(), EM))
         recordCopy(SA, EM);
     }
