Introduction
If you can not build exim.conf or associated configuration files like /etc/exim.pl.local and the error reported is regarding a perlpkg then there may be a sub function file in place that shouldn't be there or is corrupted.
Procedure
This issue is likely due to a corrupt file or duplicates in /usr/local/cpanel/etc/exim/perl/.
Either move the duplicate out of this folder or move the corrupt file out of this folder and then run the following to get the missing file downloaded again.
/usr/local/cpanel/scripts/upcp --sync --bg