Ninja: Honor $<TARGET_OBJECTS:...> source expressions

Add objects from object libraries referenced using this syntax to the
set of objects linked in a target.

Source/cmNinjaTargetGenerator.cxx

@@ -406,6 +406,17 @@ cmNinjaTargetGenerator
     this->WriteObjectBuildStatement(*si);
     }
 
+  {
+  // Add object library contents as external objects.
+  std::vector<std::string> objs;
+  this->GeneratorTarget->UseObjectLibraries(objs);
+  for(std::vector<std::string>::iterator oi = objs.begin();
+      oi != objs.end(); ++oi)
+    {
+    this->Objects.push_back(ConvertToNinjaPath(oi->c_str()));
+    }
+  }
+
   this->GetBuildFileStream() << "\n";
 }