[C++11] More 'nullptr' conversion. In some cases just using a boolean check instead of comparing to nullptr.

llvm-svn: 206243
diff --git a/llvm/lib/Analysis/InstCount.cpp b/llvm/lib/Analysis/InstCount.cpp
index 3d05556..6d81bbb 100644
--- a/llvm/lib/Analysis/InstCount.cpp
+++ b/llvm/lib/Analysis/InstCount.cpp
@@ -47,7 +47,7 @@
 
     void visitInstruction(Instruction &I) {
       errs() << "Instruction Count does not know about " << I;
-      llvm_unreachable(0);
+      llvm_unreachable(nullptr);
     }
   public:
     static char ID; // Pass identification, replacement for typeid