Fixes various compiler diagnostics

Found with LLVM 3.9.1 and then fixed the most severe categories.

src/extractor/guidance/turn_classification.cpp

@@ -32,7 +32,7 @@ classifyIntersection(Intersection intersection)
 
         DiscreteBearing last_discrete_bearing = util::guidance::BearingClass::getDiscreteBearing(
             std::round(intersection.back().bearing));
-        for (const auto road : intersection)
+        for (const auto &road : intersection)
         {
             const DiscreteBearing discrete_bearing =
                 util::guidance::BearingClass::getDiscreteBearing(std::round(road.bearing));

src/extractor/guidance/turn_lane_data.cpp

@@ -106,7 +106,7 @@ LaneDataVector laneDataFromDescription(TurnLaneDescription turn_lane_description
     // transform the map into the lane data vector
     LaneDataVector lane_data;
     lane_data.reserve(lane_map.size());
-    for (const auto tag : lane_map)
+    for (const auto &tag : lane_map)
         lane_data.push_back({tag.first, tag.second.first, tag.second.second, false});
 
     std::sort(lane_data.begin(), lane_data.end());