* sysdeps/gnu/netinet/tcp.h: Define TCP_MD5SIG, TCP_MD5SIG_MAXKEYLEN,

	struct tcp_md5sig.  Extend struct tcp_info according to recent kernels.

	* sysdeps/unix/sysv/linux/Makefile (sysdep_routines): Add eventfd,
	evetnfd_read, eventfd_write.
	* sysdeps/unix/sysv/linux/eventfd.c: New file.
	* sysdeps/unix/sysv/linux/eventfd_read.c: New file.
	* sysdeps/unix/sysv/linux/eventfd_write.c: New file.
	* sysdeps/unix/sysv/linux/sys/eventfd.h: New file.
	* sysdeps/unix/sysv/linux/Versions: Export eventfd, evetnfd_read,
	eventfd_write for GLIBC_2.7.