My notes for an Ubuntu 16 install:
sudo apt-get install libgd-dev libgraphviz-dev graphviz autoconf apache2 libapache2-mod-fcgid slapd ldap-utils expat openssl libssl-dev
Install standalone Perl for RT:
$ wget http://www.cpan.org/src/5.0/perl-5.26.3.tar.gz
$ tar -xzf perl-5.26.3.tar.gz
$ cd perl-5.26.3
$ sudo ./Configure -des -Dprefix=/opt/perl5
$ sudo make
$ sudo make test
$ sudo make install
Use new Perl install:
$ export PATH=/opt/perl5/bin:$PATH
$ which Perl
Install meta cpan:
$ wget https://cpan.metacpan.org/authors/id/M/MI/MIYAGAWA/App-cpanminus-1.7044.tar.gz
$ /opt/perl5/bin/perl Makefile.PL
$ make
$ make test
$ sudo make install
Tell RT to use metacpan:
$ export RT_FIX_DEPS_CMD='/opt/perl5/bin/cpanm --sudo --notest'
Configure RT:
./configure --enable-gd --enable-graphviz
Then you can run make fixdeps
Hope this helps!