cmLocalGenerator: add a GetObjectOutputRoot method

This will allow object locations to be changed in a single place.

Source/cmLocalGenerator.cxx

@@ -4286,6 +4286,11 @@ std::string cmLocalGenerator::GetObjectFileNameWithoutTarget(
   return this->CreateSafeUniqueObjectFileName(objectName, dir_max);
 }
 
+std::string cmLocalGenerator::GetObjectOutputRoot() const
+{
+  return this->GetCurrentBinaryDirectory();
+}
+
 std::string cmLocalGenerator::GetSourceFileLanguage(cmSourceFile const& source)
 {
   return source.GetLanguage();

Source/cmLocalGenerator.h

@@ -438,6 +438,8 @@ public:
   std::string const& GetCurrentBinaryDirectory() const;
   std::string const& GetCurrentSourceDirectory() const;
 
+  virtual std::string GetObjectOutputRoot() const;
+
   /**
    * Generate a macOS application bundle Info.plist file.
    */