[InstructionSelect] NumBlocks isn't defined in DEBUG build.

[hokein]

Summary

A follow-up fixing on http://llvm.org/viewvc/llvm-project?view=revision&revision=279905.

[bkramer]

lg

llvm/trunk/lib/CodeGen/GlobalISel/InstructionSelect.cpp

#ifndef NDEBUG
   // that it has the same layering problem, but we only use inline methods so
   // end up not needing to link against the GlobalISel library.
   if (const MachineLegalizer *MLI = MF.getSubtarget().getMachineLegalizer())
     for (const MachineBasicBlock &MBB : MF)
       for (const MachineInstr &MI : MBB)
         if (isPreISelGenericOpcode(MI.getOpcode()) && !MLI->isLegal(MI))
           reportSelectionError(MI, "Instruction is not legal");
 
+#endif
   // FIXME: We could introduce new blocks and will need to fix the outer loop.
   // Until then, keep track of the number of blocks to assert that we don't.
   const size_t NumBlocks = MF.size();
-#endif
 
   bool Failed = false;
   for (MachineBasicBlock *MBB : post_order(&MF)) {
     for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(),
                                              End = MBB->rend();
          MII != End;) {
       MachineInstr &MI = *MII++;
       DEBUG(dbgs() << "Selecting: " << MI << '\n');