Yes, you have to declare the variables. The compiler must know about the variables at compile time so it knows not to complain, and the file you require is not loaded until runtime. A solution to that might be to write a configure module that exports the variables in question.

As for the code block you show, I don't know why that should be commented out in production code. The only thing I see that should only be used during development is fatalsToBrowser — but all the rest applies, including use CGI::Carp; itself, since that will make your server error logs more informative.