Use nullptr instead of NULL for variadic sentinels

Windows defines NULL to 0, which when used as an argument to a variadic
function, is not a null pointer constant. As a result, Clang's
-Wsentinel fires on this code. Using '0' would be wrong on most 64-bit
platforms, but both MSVC and Clang make it work on Windows. Sidestep the
issue with nullptr.

llvm-svn: 221940
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 4b48d7d..57a4f0b 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -364,7 +364,7 @@
 
 /// IsConstantOne - Return true only if val is constant int 1
 static bool IsConstantOne(Value *val) {
-  assert(val && "IsConstantOne does not work with NULL val");
+  assert(val && "IsConstantOne does not work with nullptr val");
   const ConstantInt *CVal = dyn_cast<ConstantInt>(val);
   return CVal && CVal->isOne();
 }
@@ -419,7 +419,7 @@
   Value *MallocFunc = MallocF;
   if (!MallocFunc)
     // prototype malloc as "void *malloc(size_t)"
-    MallocFunc = M->getOrInsertFunction("malloc", BPTy, IntPtrTy, NULL);
+    MallocFunc = M->getOrInsertFunction("malloc", BPTy, IntPtrTy, nullptr);
   PointerType *AllocPtrType = PointerType::getUnqual(AllocTy);
   CallInst *MCall = nullptr;
   Instruction *Result = nullptr;
@@ -492,7 +492,7 @@
   Type *VoidTy = Type::getVoidTy(M->getContext());
   Type *IntPtrTy = Type::getInt8PtrTy(M->getContext());
   // prototype free as "void free(void*)"
-  Value *FreeFunc = M->getOrInsertFunction("free", VoidTy, IntPtrTy, NULL);
+  Value *FreeFunc = M->getOrInsertFunction("free", VoidTy, IntPtrTy, nullptr);
   CallInst* Result = nullptr;
   Value *PtrCast = Source;
   if (InsertBefore) {