Sorry, I guess I did leave that as a doubt. All of the libraries developed in-house are in lib/perl and I ran

find lib/perl -exec grep __DIE__ {} \; -print
[download]

getting back absolutely no results. It was thus that I came to the conclusion that the __DIE__ handler is coming as a secondary effect of including an in-house library that must include some third party library that installs a custom __DIE__ handler.