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

llvm-svn: 209389
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 6aeb9c6..2ba9450 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1955,7 +1955,7 @@
     }
 
     IntrusiveRefCntPtr<vfs::FileSystem> FS =
-        vfs::getVFSFromYAML(Buffer.release(), /*DiagHandler*/0);
+        vfs::getVFSFromYAML(Buffer.release(), /*DiagHandler*/nullptr);
     if (!FS.getPtr()) {
       Diags.Report(diag::err_invalid_vfs_overlay) << File;
       return IntrusiveRefCntPtr<vfs::FileSystem>();