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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206243 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/MemoryBuiltins.h

@@ -233,7 +233,7 @@ class ObjectSizeOffsetEvaluator
   bool RoundToAlign;
 
   SizeOffsetEvalType unknown() {
-    return std::make_pair((Value*)0, (Value*)0);
+    return std::make_pair(nullptr, nullptr);
   }
   SizeOffsetEvalType compute_(Value *V);