[PrologEpilogInserter] Add some debug output for callee-save frame object allocation

[mcrosier]

LGTM.

lib/CodeGen/PrologEpilogInserter.cpp

for (unsigned i = MinCSFrameIndex; i <= MaxCSFrameIndex; ++i) {
       // If the stack grows down, we need to add the size to find the lowest
       // address of the object.
       Offset += MFI->getObjectSize(i);
 
       unsigned Align = MFI->getObjectAlignment(i);
       // Adjust to alignment boundary
       Offset = alignTo(Offset, Align, Skew);
 
+      DEBUG(dbgs() << "alloc FI(" << i << ") at SP[" << -Offset << "]\n");
       MFI->setObjectOffset(i, -Offset);        // Set the computed offset
     }
   } else {
     int MaxCSFI = MaxCSFrameIndex, MinCSFI = MinCSFrameIndex;
     for (int i = MaxCSFI; i >= MinCSFI ; --i) {
       unsigned Align = MFI->getObjectAlignment(i);
       // Adjust to alignment boundary
       Offset = alignTo(Offset, Align, Skew);
 
+      DEBUG(dbgs() << "alloc FI(" << i << ") at SP[" << Offset << "]\n");
       MFI->setObjectOffset(i, Offset);
       Offset += MFI->getObjectSize(i);
     }
   }
 
   unsigned MaxAlign = MFI->getMaxAlignment();
 
   // Make sure the special register scavenging spill slot is closest to the