[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@206252 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/BasicBlock.cpp

@@ -81,7 +81,7 @@ BasicBlock::~BasicBlock() {
     }
   }
 
-  assert(getParent() == 0 && "BasicBlock still linked into the program!");
+  assert(getParent() == nullptr && "BasicBlock still linked into the program!");
   dropAllReferences();
   InstList.clear();
 }