cmGeneratorTarget: Add method to get the object file directory

Add a `GetObjectDirectory` method to get the target's object file
directory for a specific configuration.

Source/cmGeneratorTarget.cxx

@@ -3254,6 +3254,19 @@ std::string cmGeneratorTarget::GetPDBName(const std::string& config) const
   return prefix + base + ".pdb";
 }
 
+std::string cmGeneratorTarget::GetObjectDirectory(
+  std::string const& config) const
+{
+  std::string obj_dir =
+    this->GlobalGenerator->ExpandCFGIntDir(this->ObjectDirectory, config);
+#if defined(__APPLE__)
+  // find and replace $(PROJECT_NAME) xcode placeholder
+  const std::string projectName = this->LocalGenerator->GetProjectName();
+  cmSystemTools::ReplaceString(obj_dir, "$(PROJECT_NAME)", projectName);
+#endif
+  return obj_dir;
+}
+
 void cmGeneratorTarget::GetTargetObjectNames(
   std::string const& config, std::vector<std::string>& objects) const
 {

Source/cmGeneratorTarget.h

@@ -369,6 +369,10 @@ public:
       time config name placeholder if needed for the generator.  */
   std::string ObjectDirectory;
 
+  /** Full path with trailing slash to the top-level directory
+      holding object files for the given configuration.  */
+  std::string GetObjectDirectory(std::string const& config) const;
+
   void GetAppleArchs(const std::string& config,
                      std::vector<std::string>& archVec) const;