[DetectDeadLanes] Enable machine verification after this pass

[foad]

Summary

Machine verification after DetectDeadLanes has been disabled since the
pass was first added in D18427, but I guess this was just due to copy-
and-paste. Enabling it does not show any problems in check-llvm in an
LLVM_ENABLE_EXPENSIVE_CHECKS build.

[MatzeB]

I'm always happy when we can cover more parts of CodeGen with the machine verifier. Let's hope this sticks. LGTM

llvm/lib/CodeGen/TargetPassConfig.cpp

void TargetPassConfig::addFastRegAlloc() {
 
   addRegAssignAndRewriteFast();
 }
 
 /// Add standard target-independent passes that are tightly coupled with
 /// optimized register allocation, including coalescing, machine instruction
 /// scheduling, and register allocation itself.
 void TargetPassConfig::addOptimizedRegAlloc() {
-  addPass(&DetectDeadLanesID, false);
+  addPass(&DetectDeadLanesID);
 
   addPass(&ProcessImplicitDefsID, false);
 
   // LiveVariables currently requires pure SSA form.
   //
   // FIXME: Once TwoAddressInstruction pass no longer uses kill flags,
   // LiveVariables can be removed completely, and LiveIntervals can be directly
   // computed. (We still either need to regenerate kill flags after regalloc, or