Here's a thought, try

$prog_name = eval("\$\x18"); # $^X
$exec_type = `file $prog_name`;
if($exec_type =~ /32/)
  {
    print "32 bit\n";
  }
elsif($exec_type =~ /64/)
  {
    print "64 bit\n";
  }
else
  {
    print "Cant unpick from $exec_type\n"
  }
[download]

(Untested code)

This would be if you are worried about linking to shared libraries (eg a 32 bit version of Perl won't load a 64 bit shared library under Solaris)

Update: Corrected stupid use of $0 to $^X