Fix the Guess-DSO-flags-from-Perl stuff in src/Configure: "perl" was used

instead of "$PERL" which contains the correctly determined Perl interpreter
(important for instance on systems where "perl" and "perl5" exists, like BSDI
or FreeBSD, etc).

PR: 2505


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@81621 13f79535-47bb-0310-9956-ffa450edef68