Use nullptr to silence -Wsentinel when self-hosting on Windows

Richard rejected my Sema change to interpret an integer literal zero in
a varargs context as a null pointer, so -Wsentinel sees an integer
literal zero and fires off a warning. Only CodeGen currently knows that
it promotes integer literal zeroes in this context to pointer size on
Windows.  I didn't want to teach -Wsentinel about that compatibility
hack. Therefore, I'm migrating to C++11 nullptr.

llvm-svn: 223079
diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
index 05fc8631..fa89033 100644
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -745,7 +745,7 @@
   EmitBlock(lpad);
 
   llvm::LandingPadInst *LPadInst =
-    Builder.CreateLandingPad(llvm::StructType::get(Int8PtrTy, Int32Ty, NULL),
+    Builder.CreateLandingPad(llvm::StructType::get(Int8PtrTy, Int32Ty, nullptr),
                              getOpaquePersonalityFn(CGM, personality), 0);
 
   llvm::Value *LPadExn = Builder.CreateExtractValue(LPadInst, 0);
@@ -1557,7 +1557,7 @@
   // Tell the backend that this is a landing pad.
   const EHPersonality &Personality = EHPersonality::get(CGM);
   llvm::LandingPadInst *LPadInst =
-    Builder.CreateLandingPad(llvm::StructType::get(Int8PtrTy, Int32Ty, NULL),
+    Builder.CreateLandingPad(llvm::StructType::get(Int8PtrTy, Int32Ty, nullptr),
                              getOpaquePersonalityFn(CGM, Personality), 0);
   LPadInst->addClause(getCatchAllValue(*this));
 
@@ -1633,7 +1633,7 @@
   llvm::Value *Sel = getSelectorFromSlot();
 
   llvm::Type *LPadType = llvm::StructType::get(Exn->getType(),
-                                               Sel->getType(), NULL);
+                                               Sel->getType(), nullptr);
   llvm::Value *LPadVal = llvm::UndefValue::get(LPadType);
   LPadVal = Builder.CreateInsertValue(LPadVal, Exn, 0, "lpad.val");
   LPadVal = Builder.CreateInsertValue(LPadVal, Sel, 1, "lpad.val");