Currently, Parrot's Configure.pl leans heavily on Perl 5's Configure script. A lot of the settings Configure.pl uses are read from the Config.pm module, which is generated by Perl 5's Configure.
Unfortunately, the real version of Parrot can't depend on having Perl 5 around. That message is essentially an order to start copying tests from Perl 5's Configure into Configure.pl.
Understand, Configure.pl is written in Perl, while Configure is a shell script. (Shell scripts are essentially lists of commands to run--they're the Unix equivalent of batch files, except that they're a hell of a lot more powerful, and quite a bit more complex to match.)
Shell scripts are a "language" I've never used, outside of .bashrc and friends (the Unix autoexec.bat). And Configure is a 21,536 line shell script, and a total mess because it has to be portable to virtually any variety of Unix.
That doesn't count the platform-specific hints files, either.