Update aosp/master LLVM for rebase to r222494.

Change-Id: Ic787f5e0124df789bd26f3f24680f45e678eef2d
diff --git a/lib/CodeGen/ShadowStackGC.cpp b/lib/CodeGen/ShadowStackGC.cpp
index f7c64da..0be00f0 100644
--- a/lib/CodeGen/ShadowStackGC.cpp
+++ b/lib/CodeGen/ShadowStackGC.cpp
@@ -144,7 +144,7 @@
         LLVMContext &C = F.getContext();
         BasicBlock *CleanupBB = BasicBlock::Create(C, CleanupBBName, &F);
         Type *ExnTy = StructType::get(Type::getInt8PtrTy(C),
-                                      Type::getInt32Ty(C), NULL);
+                                      Type::getInt32Ty(C), nullptr);
         Constant *PersFn =
           F.getParent()->
           getOrInsertFunction("__gcc_personality_v0",