compat.h: Add SOCK_CLOEXEC and SOCK_NONBLOCK for older glibc.

This patch fixes these build errors with glibc before 2.9.

syscalls/socket.c: In function ‘gen_socket_args’:
syscalls/socket.c:82: error: ‘SOCK_CLOEXEC’ undeclared (first use in this function)
syscalls/socket.c:82: error: (Each undeclared identifier is reported only once
syscalls/socket.c:82: error: for each function it appears in.)
syscalls/socket.c:84: error: ‘SOCK_NONBLOCK’ undeclared (first use in this function)

Signed-off-by: Vinson Lee <vlee@twitter.com>