Do we need generate.pl to wipe/recreate the download dir every time?

I'm regenerating the Dockerfiles and I noticed it takes ages. 10 years ago it was added via 5150798c. I'm not 100% if we still need this tear-down, tear-up strategy.

Perhaps we can add some kind of flag to generate.pl to keep the old behaviour, but this would speed up regenerations.

  {
    my $dir = "$downloads/perl-$release->{version}";
    qx{rm -fR $dir};
    mkdir $dir or die "Couldn't create $dir";
    qx{
      tar -C "$downloads" -xf $dir.tar.gz &&\
      cd $dir &&\
      chown -R \$(id -u):\$(id -g) . &&\
      git init &&\
      git add . &&\
      git commit -m tmp
    };
    die "Couldn't create a temp git repo for $release->{version}" if $? != 0;
    Devel::PatchPerl->patch_source($release->{version}, $dir);
    $patch = qx{
      cd $dir && git -c 'diff.mnemonicprefix=false' diff
    };
    die "Couldn't create a Devel::PatchPerl patch for $release->{version}" if $? != 0;
  }

I often see cat *.patch errors in the logs when an image is build, so the slowdown seems not justifiable.

Start by reviewing the directory teardown and temporary Git repository logic in generate.pl, then reproduce the slow Dockerfile regeneration and inspect the reported cat *.patch errors. Done means the need to wipe and recreate the download directory is established and any changed behavior preserves a way to retain the old behavior if required.