Refactor X68k input device handling to remove SIGIO based event processing.

The keyboard and pointer input events are now processed directly
using fd event notifications registered via DIX SetNotifyFd(),
instead of the legacy SIGIO-based asynchronous I/O.

Merge AbortDDX() into ddxGiveUp() as other upstream DDX servers.

https://gitlab.freedesktop.org/xorg/xserver/-/commit/a23eba2a91024d27da45e5aee1f4215f7ec2ae82
> These are so close to identical that most DDXes implement one in terms
> of the other. All the relevant cases can be distinguished by the error
> code, so merge the functions together to make things simpler.

couple of changes needed for xorg-server 21.1.4.

- AbortDDX() is removed, make it static to avoid code churn since
it is used by internal code now
- LegalModifier() is gone
- if the PRESENT extension isn't included, don't enable the
-fakescreenfps option since it require PRESENT.

fixes builds for sun3 and x68k.

add dummy ddxInputThreadInit() if INPUTTHREAD is defined.
fixes sun3 build and should fix x68k build too.

Call LogInit() for logging to /var/log/X68k.%s.log as Xorg and Xsun servers.

TAB/space cleanup.

Normalize #include paths.

Add a stub for miinitext of GLX.

As per upstream commits for Xnest:
https://cgit.freedesktop.org/xorg/xserver/commit/?id=67c303fff303f94b62f03a76de97116c6ebcfda9

Note GLXEXT is defined as 1 in xorg-server/include/xorg-server.h
(i.e. /usr/X11R7/include/xorg/xorg-server.h) so no proper way to
disable it on building MD servers per ${MACHINE} basis.

Pull changes of x68kInit.c rev 1.3 from xorg-server.old.

https://mail-index.netbsd.org/source-changes/2020/07/18/msg119473.html
> Use AllocDevicePair() to initialize input devices in InitInput().

Untested, but I'll re-visit on migrating to HAVE_XORG_SERVER_VER=120.

Remove clause 3 and 4 from X68k server files written by Yasushi Yamasaki.

I've finally contacted with Yamasaki-san and he kindly answered
"no objection to change them to 2 clause license" in private mail.
Diffs to be committed have also been confirmed by him.
We appreciate all his contribution to early NetBSD/x68k.

Pull more changes from Xnest to adapt X68k to Xorg server 1.18.

- use QueueKeyboardEvents() and QueuePointerEvents() which are provided
by dix/getevents.c, instead of raw mieqEnqueue() with uninitialized
local InternalEvent
- remove now actually unused local InternalEvent
- explicitly call mieqFini() in DDX CloseInput()

Confirmed working on XM6i, and "please commit" from mrg@.

port to xorg-server 1.18. builds and may work, but not tested.

Port the ancient Xsun based monolithic MD X68k server to X11R7, like Xnest.

Most diffs (API changes from xfree to xorg and some WARNSfy)
are mechanical. Confirmed working on X68030 and XM6i.

See my post on port-x68k@ for details:
http://mail-index.netbsd.org/port-x68k/2014/02/27/msg000043.html