getopt_long: Copy over the implementation from netbsd.

getopt_long: Copy over the implementation from netbsd.

Windows does not have a getopt_long function. This commit
copies over the getopt_long implementation from netbsd with
some minor modifications and is used only on Windows platform.

Modifications on top of the version in NetBSD repo.
* Remove header files not available in Visual Studio.
* Remove some unwanted #defines.
* Add Open vSwitch specific header files like config.h, vlog.h, util.h
* Add the following #define's
define __UNCONST(a)    ((void *)(unsigned long)(const void *)(a))
define _DIAGASSERT(q) ovs_assert(q)
define warnx VLOG_WARN
* Add extern declaration in getopt.h for optarg, optind.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>