[Target] Use DenseSet instead of DenseMap (NFC)

This patch uses DenseSet instead of DenseMap.  Note that the set of
Registers that map to true without this patch is the same as the set
of Registers that are present in the set with this patch.  This patch
is inspired by:

  commit d7879e5
  Author: Craig Topper <[email protected]>
  Date:   Wed Mar 19 08:32:09 2025 -0700

Author: kazutakahirata

llvm/lib/Target/VE/VEISelLowering.cpp

@@ -2645,15 +2645,15 @@ VETargetLowering::emitSjLjDispatchBlock(MachineInstr &MI,
       if (!II.isCall())
         continue;
 
-      DenseMap<Register, bool> DefRegs;
+      DenseSet<Register> DefRegs;
       for (auto &MOp : II.operands())
         if (MOp.isReg())
-          DefRegs[MOp.getReg()] = true;
+          DefRegs.insert(MOp.getReg());
 
       MachineInstrBuilder MIB(*MF, &II);
       for (unsigned RI = 0; SavedRegs[RI]; ++RI) {
         Register Reg = SavedRegs[RI];
-        if (!DefRegs[Reg])
+        if (!DefRegs.contains(Reg))
           MIB.addReg(Reg, RegState::ImplicitDefine | RegState::Dead);
       }
 

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -37430,15 +37430,15 @@ X86TargetLowering::EmitSjLjDispatchBlock(MachineInstr &MI,
       if (!II.isCall())
         continue;
 
-      DenseMap<Register, bool> DefRegs;
+      DenseSet<Register> DefRegs;
       for (auto &MOp : II.operands())
         if (MOp.isReg())
-          DefRegs[MOp.getReg()] = true;
+          DefRegs.insert(MOp.getReg());
 
       MachineInstrBuilder MIB(*MF, &II);
       for (unsigned RegIdx = 0; SavedRegs[RegIdx]; ++RegIdx) {
         Register Reg = SavedRegs[RegIdx];
-        if (!DefRegs[Reg])
+        if (!DefRegs.contains(Reg))
           MIB.addReg(Reg, RegState::ImplicitDefine | RegState::Dead);
       }