Apparently memfd_create() is newish in glibc, and oss-fuzz
uses Ubuntu 16.04 as base for its docker images, which doens't
yet have memfd_create(). But, not to worry, it does have the syscall
define and that's all we really need :/
SOCK_NONBLOCK is a linux-ism that serenity and linux support. For lagom
builds, we use ioctl/fcntl to get a non-blocking socket the old
fashioned way. Some file re-org unhid the fcntl.h dependency of TcpServer,
so add the header explicitly.
This API was a mostly gratuitous deviation from POSIX that gave up some
portability in exchange for avoiding the occasional strlen().
I don't think that was actually achieving anything valuable, so let's
just chill out and have the same open() API as everyone else. :^)
