Adding a file for Perl (5.20.0 and 5.18.2)

The referenced repo has 4 directories right now, 2 for
each version of Perl.  One has command line options
just for 64-bit compilation (which would actually be turned
on by default anyway, but I wanted to be explicit about it),
and the other will also enable threads.  Threads are generally
discouraged, so they specifically need to be opted into.