[Statepoint] Fix StatepointLoweringInfo::GCTransitionArgs initialization

[dantrushin]

Summary

In method SelectionDAGBuilder::LowerStatepoint, array SI.GCTransitionArgs
is initialized from wrong part of ImmutableStatepoint class.
We copy gc args instead of transitions args.

llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

for (const GCRelocateInst *Relocate : ISP.getRelocates()) {
     if (Seen.insert(DerivedSD).second) {
       SI.Bases.push_back(Relocate->getBasePtr());
       SI.Ptrs.push_back(Relocate->getDerivedPtr());
     }
   }
 
   SI.GCArgs = ArrayRef<const Use>(ISP.gc_args_begin(), ISP.gc_args_end());
   SI.StatepointInstr = ISP.getInstruction();
-  SI.GCTransitionArgs =
-      ArrayRef<const Use>(ISP.gc_args_begin(), ISP.gc_args_end());
+  SI.GCTransitionArgs = ArrayRef<const Use>(ISP.gc_transition_args_begin(),
+                                            ISP.gc_transition_args_end());
   SI.ID = ISP.getID();
   SI.DeoptState = ArrayRef<const Use>(ISP.deopt_begin(), ISP.deopt_end());
   SI.StatepointFlags = ISP.getFlags();
   SI.NumPatchBytes = ISP.getNumPatchBytes();
   SI.EHPadBB = EHPadBB;
 
   SDValue ReturnValue = LowerAsSTATEPOINT(SI);