tools/gn: Change auto to not deduce raw pointers.

tools/gn/xcode_writer.cc

Index: tools/gn/xcode_writer.cc
diff --git a/tools/gn/xcode_writer.cc b/tools/gn/xcode_writer.cc
index e07633954df6142eb95e132207c16661d99b4623..d60f4f77d0c365cdad68c6d3d6c752f552816ad9 100644
--- a/tools/gn/xcode_writer.cc
+++ b/tools/gn/xcode_writer.cc
@@ -419,7 +419,7 @@ void XcodeWriter::WriteProjectContent(std::ostream& out, PBXProject* project) {
               [](const PBXObject* a, const PBXObject* b) {
                 return a->id() < b->id();
               });
-    for (const auto& object : pair.second) {
+    for (auto* object : pair.second) {
       object->Print(out, 2);
     }
     out << "/* End " << ToString(pair.first) << " section */\n";