[CodeGen] Avoid access after runtime

Insts must be destroyd before xParent
or it can read it with stack like this:
   0 in llvm::MachineInstr::getMF() const MachineInstr.cpp:637:3
   1 in getMF MachineInstr.h:302:50
   2 in removeNodeFromList MachineBasicBlock.cpp:163:32

llvm/include/llvm/CodeGen/MachineBasicBlock.h

@@ -109,10 +109,10 @@ class MachineBasicBlock
 private:
   using Instructions = ilist<MachineInstr, ilist_sentinel_tracking<true>>;
 
-  Instructions Insts;
   const BasicBlock *BB;
   int Number;
   MachineFunction *xParent;
+  Instructions Insts;
 
   /// Keep track of the predecessor / successor basic blocks.
   std::vector<MachineBasicBlock *> Predecessors;