If you're a developer, Makefile.PL will pack `cpanm` from script/cpanm.PL and then copy that file to `bin/cpanm`.
You can pretend to be an author by running it with:
perl Makefile.PL --author
You should install local::lib, Parse::CPAN::Meta, Module::Metadata, App::FatPacker and HTTP::Lite before doing so.
Module::Metadata is not available on CPAN as of this writing, get it from:
Do not commit the changes to `cpanm` standalone executable. We only commit changes to this file whenever we tag a new CPAN release.