[MachineCombiner] Removal of dangling DBG_VALUES after combining [20598]

This is a cleaner solution to the problem described in r215431.
When instructions are combined a dangling DBG_VALUE is removed.
This resolves bug 20598.

llvm-svn: 215587
diff --git a/llvm/lib/CodeGen/MachineCombiner.cpp b/llvm/lib/CodeGen/MachineCombiner.cpp
index 032b4ee..aeb864e 100644
--- a/llvm/lib/CodeGen/MachineCombiner.cpp
+++ b/llvm/lib/CodeGen/MachineCombiner.cpp
@@ -380,7 +380,7 @@
             MBB->insert((MachineBasicBlock::iterator) & MI,
                         (MachineInstr *)InstrPtr);
           for (auto *InstrPtr : DelInstrs)
-            InstrPtr->eraseFromParent();
+            InstrPtr->eraseFromParentAndMarkDBGValuesForRemoval();
 
           Changed = true;
           ++NumInstCombined;