Yeah, actually the biggest driver for this is cpan testers :-) My error message is "Author is lazy and requires 64-bit perl integers". But there's no way I know to exclude the 32-bit perls, and then I get those pesky failures on my testers matrix. And then I was thinking "Maybe I could try not being lazy and actually make it work on 32-bit perls?"

This is in fact the same reason I fixed ELF::Writer to support 32-bit perls and perls before 5.10, but yes I know I could just declare a minimum perl version and not need to see errors on 5.8 related to pack('Q<'). But I already implemented the workaround for pack('Q<'), so seems a shame to not keep using it.

But there's no way I know to exclude the 32-bit perls

You would just want your CPU-x86_64-InstructionWriter-0.002 Makefile.PL to begin with:

use strict;
use warnings;

use 5.010000;

use ExtUtils::MakeMaker;

if($Config::Config{ivsize} != 8) {
  warn "This module requires 64-bit integers";
  exit 0;
}

# existing code then follows, unaltered.
[download]

I don't know how you achieve that alteration using Dist::Zilla to generate your Makefile.PL, but cpantesters would then report your module as "NA" instead of "FAIL".
Anyway, adding support for 32-bit integers might be a more interesting exercise ;-)

Cheers,
Rob