FreeBSD (and other *BSDs) do not have stable syscall numbers, so
drop no-op checks for it and add a note to use Inline::C,
instead. Drop an implicit return for the syscall.ph loading
while we're at it, too.
On Linux, epoll_create(2) ignores the size arg since Linux
2.6.8, so just hard code it to some non-zero value.
On a side note, we can probably drop epoll_create(2) support
soon and just use epoll_create1(2) which appeared in 2.6.27+
(2008-10-09). Our userspace (Perl and git) requirements are
already further ahead.