Fix gcc5 build failure (NFC)

[mehdi_amini]

Summary

The loop index was shadowing the container name.
It seems that we can just not use a for-range loop here since there is
an induction variable anyway.

llvm/lib/Target/AMDGPU/AMDGPUCallLowering.cpp

void AMDGPUCallLowering::processSplitArgs(
     CallingConv::ID CallConv, bool IsOutgoing,
     SplitArgTy PerformArgSplit) const {
   LLVMContext &Ctx = OrigArg.Ty->getContext();
   const SITargetLowering &TLI = *getTLI<SITargetLowering>();
 
   // FIXME: This is mostly nasty pre-processing before handleAssignments. Most
   // of this should be performed by handleAssignments.
 
-  int SplitIdx = 0;
-  for (const ArgInfo &SplitArg : SplitArg) {
+  for (int SplitIdx = 0, e = SplitArg.size(); SplitIdx != e; ++SplitIdx) {
+    const ArgInfo &CurSplitArg = SplitArg[SplitIdx];
     Register Reg = OrigArg.Regs[SplitIdx];
-    EVT VT = EVT::getEVT(SplitArg.Ty);
-    LLT LLTy = getLLTForType(*SplitArg.Ty, DL);
+    EVT VT = EVT::getEVT(CurSplitArg.Ty);
+    LLT LLTy = getLLTForType(*CurSplitArg.Ty, DL);
 
     unsigned NumParts = TLI.getNumRegistersForCallingConv(Ctx, CallConv, VT);
     MVT RegVT = TLI.getRegisterTypeForCallingConv(Ctx, CallConv, VT);
 
     if (NumParts == 1) {
       // No splitting to do, but we want to replace the original type (e.g. [1 x
       // double] -> double).
-      SplitArgs.emplace_back(Reg, SplitArg.Ty, OrigArg.Flags, OrigArg.IsFixed);
-
-      ++SplitIdx;
+      SplitArgs.emplace_back(Reg, CurSplitArg.Ty, OrigArg.Flags,
+                             OrigArg.IsFixed);
       continue;
     }
 
     SmallVector<Register, 8> SplitRegs;
     Type *PartTy = EVT(RegVT).getTypeForEVT(Ctx);
     LLT PartLLT = getLLTForType(*PartTy, DL);
     MachineRegisterInfo &MRI = *B.getMRI();
 
     // FIXME: Should we be reporting all of the part registers for a single
     // argument, and let handleAssignments take care of the repacking?
     for (unsigned i = 0; i < NumParts; ++i) {
       Register PartReg = MRI.createGenericVirtualRegister(PartLLT);
       SplitRegs.push_back(PartReg);
       SplitArgs.emplace_back(ArrayRef<Register>(PartReg), PartTy, OrigArg.Flags);
     }
 
     PerformArgSplit(SplitRegs, Reg, LLTy, PartLLT, SplitIdx);
-
-    ++SplitIdx;
   }
 }
 
 // TODO: Move to generic code
 static void unpackRegsToOrigType(MachineIRBuilder &B,
                                  ArrayRef<Register> DstRegs,
                                  Register SrcReg,
                                  const CallLowering::ArgInfo &Info,