Perfect, thank you!

I ended up with doing some extra magic in BEGIN, to automate those compile steps (.cpp and .h files in same directory):

#!/usr/bin/env perl

use v5.38;
use strict;
use warnings;

use Carp;
use Cwd;
use Array::Contains;

my $dir;
my $verbose;
BEGIN {
    $dir = getcwd;
    print "Working directory: $dir\n";

    $verbose = 0;
    if(contains('-v', \@ARGV)) {
        $verbose = 1;
    }
    
    # ---- Poor mans Makefile ---
    if(contains('--clean', \@ARGV)) {
        print "Cleaning up\n";
        my $cmd = 'rm -rf _Inline xkcd.o libxkcd.a';
        print "$cmd\n" if($verbose);
        `$cmd`;
        exit(0);
    }

    print "Compiling library...\n";
    foreach my $cmd ('g++ -c xkcd.cpp', 'ar -rc libxkcd.a xkcd.o') {
        print "$cmd\n" if $verbose;
        `$cmd`;
    }
    # ---- Poor mans Makefile ---

};

use Inline 'CPP';
use Inline CPP => Config =>
  BUILD_NOISY => $verbose,
  INC => '-I' . $dir,
  LIBS => '-L' . $dir . ' -lxkcd',
;
 
for(1..3) {
    print "XKCD Dice roll: ", cast_die(), "\n";
}
 
__END__
__CPP__

#include "xkcd.h"
 
int cast_die() {
    int rolled = xkcd_dice_roll();
    return rolled;
}
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Hmm, i also tested without the empty lines at the bottom of the files and it worked fine. But i dimly remember having the same (or similar) issue to yours on another project.