I'd create a module for each platform, and load the appropriate module.

sub get_sys_info {
   if ($^O eq 'Win32') {
      require My::SystemInfo::Win32;
      return My::SystemInfo::Win32->new();
   } else {
      require My::SystemInfo::Unix;
      return My::SystemInfo::Unix->new();
   }
}

my $sys_info = get_sys_info();
... $sys_info->wdpi ...
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