[C++11] Use 'nullptr'. Frontend edition.

llvm-svn: 209389
diff --git a/clang/lib/Frontend/DependencyGraph.cpp b/clang/lib/Frontend/DependencyGraph.cpp
index 4bff3db..051b7f9 100644
--- a/clang/lib/Frontend/DependencyGraph.cpp
+++ b/clang/lib/Frontend/DependencyGraph.cpp
@@ -79,7 +79,7 @@
   SourceManager &SM = PP->getSourceManager();
   const FileEntry *FromFile
     = SM.getFileEntryForID(SM.getFileID(SM.getExpansionLoc(HashLoc)));
-  if (FromFile == 0) 
+  if (!FromFile)
     return;
 
   Dependencies[FromFile].push_back(File);