Peeking in the source, it turns out there's a C variable that holds the count. (Not very surprising...). Here's an Inline::C program giving you access to it:

#!/usr/bin/perl

use strict;
use warnings;

use Inline 'C';


eval 'print "Hello, world\n"';
printf "Sequence number: %d\n", gimmi ();
eval 'print "Hello, earthlings\n"';
printf "Sequence number: %d\n", gimmi ();

__END__
__C__
int gimmi () {
    return (PL_evalseq);
}
[download]

That that if you run this the first time, you'll get high numbers, but that's because Inline and/or Inline::C will do some evalling as well. After that, the count starts at 2, probably also because of some evalling inside Inline and/or Inline::C.

Abigail