Brute-forced a set of changes which allowed
 make unicode-encapsulate
to work
 1) Patched make-mswin-unicode.pl to match macros with pointer return types;
 2) Updated intl-encap-win32.c to deal with
    a) added functions;
    b) refactoring of w32api include files.

Renamed DEVICE_TYPE to DEVICE_TYPE_X in device-impl.h and everywhere
it is used to avoid collision with DEVICE_TYPE in winioctl.h

Minimal fixes to get to compile wrt int vs. intptr_t in
 event-msw.c

event-msw.c:67:3: error: #error Something is wrong -- you are neither
Windows native (possibly MinGW) nor Cygwin.  # error Something is
wrong -- you are neither Windows native (possibly MinGW) nor Cygwin.

Ah, need a more up-to-date config.{sub,guess}, got one from somewhere
dated timestamp='2013-06-10'

Copy src/s/cygwin32.h to cygwin64.h and src/m/intel386.h to x86_64.h

And a configure.ac which recognises cygwin64
 
Remove cygwin_conv_to_posix_path from lib-src/gnuclient.c

Replace calls to qxeGetWindowLong(... GWL_..) with
qxeGetWindowLongPtr(... GWLP_...) (w. LONG_PTR result if used)
after re-making unicode-encapsulate
And one LONG l = qxeGetWindowLong (hwnd, XWL_FRAMEOBJ) to LONG_PTR l = qxeGetWindowLongPtr (hwnd, XWL_FRAMEOBJ)

Ah, several bugs in new header files in w32api, required some
additions to wfun_re in make-mswin-unicode.pl

That's enough to get event-msw.c to compile, although there are some
size-related warnings.

similar problem in frame-msw.c:
 qxeSetClassLong (FRAME_MSWINDOWS_HANDLE (f), GCL_HICON

and in glyphs-msw.c:
 qxeGetWindowLong
  (FRAME_MSWINDOWS_HANDLE (XFRAME (frame)),
   GWL_HINSTANCE),

and scrollbar-msw.c
also
      (void *) opaque =
	 (void *)qxeGetWindowLong (SCROLLBAR_MSW_HANDLE (sb), GWL_USERDATA);

        LONG_PTR opaque =
	 qxeGetWindowLongPtr (SCROLLBAR_MSW_HANDLE (sb), GWLP_USERDATA);

and dialog-msw.c:197:31: error: ‘DWL_USER’ undeclared (first use in this function)
       qxeSetWindowLong (hwnd, DWL_USER, l_param);

Compiles all the way through, links OK, temacs runs!
Build completes
xemacs -nw works
but xemacs as such does not:
 > ./xemacs
  Fatal error: assertion failed, file event-msw.c, line 4149, !NILP (Vmswindows_frame_being_created)
--------------
console-msw.c:116:3: warning: format '%ld' expects argument of type
'long int', but argument 3 has type 'DWORD' [-Wformat=]
 resolution: cast the DWORDs to long
----
event-msw.c: In function 'mswindows_wnd_proc':
event-msw.c:2741:6: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
     ((LCID) GetKeyboardLayout (0) & 0xFFFF),
            cast to intptr_t first

event-msw.c:2825:50: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
       virtual_key = qxeMapVirtualKeyEx (scan, 1, (HKL) lcid);
                                                     cast to intptr_t first
                                                  ^
event-msw.c:2839:6: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
      (HKL) lcid);
     ^    ditto

event-msw.c:2861:7: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
       (HKL) lcid);
       ^   ditto

[I _really_ don't understand the size hacking going on between LCIDs
  and HKLs here!]
event-msw.c: In function 'emacs_mswindows_remove_timeout':
event-msw.c:4200:6: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
      (void *) id, MECR_DEALLOCATE_EVENT);
      ^
  This is a hack!!! Use intptr_t instead, still a hack.


frame-msw.c: In function ‘mswindows_init_frame_1’:
frame-msw.c:274:41: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
  qxeSetWindowLong (hwnd, XWL_FRAMEOBJ, (LONG)STORE_LISP_IN_VOID (frame_obj));
                                          intptr_t

frame-msw.c: In function ‘mswindows_get_mouse_position’:
frame-msw.c:554:32: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
   *frame = GET_LISP_FROM_VOID ((void *) qxeGetWindowLong (hwnd, XWL_FRAMEOBJ));
                                         qxeGetWindowLongPtr (hwnd, XWL_FRAMEOBJ

frame-msw.c: In function ‘mswindows_get_frame_parent’:
frame-msw.c:822:36: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
       parent = GET_LISP_FROM_VOID ((void *) qxeGetWindowLong (hwnd, XWL_FRAMEOBJ));
             ditto

glyphs-msw.c: In function 'mswindows_widget_instantiate':
glyphs-msw.c:2261:8: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
        (HMENU)id,       /* No menu */
  intptr_t id = -1;

menubar-msw.c: In function 'empty_menu':
menubar-msw.c:98:24: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
 #define EMPTY_ITEM_ID ((UINT)STORE_LISP_IN_VOID (Qunbound))
menubar-msw.c:181:49: note: in expansion of macro 'EMPTY_ITEM_ID'
     qxeAppendMenu (menu, MF_STRING | MF_GRAYED, EMPTY_ITEM_ID,
 resolved:#define EMPTY_ITEM_ID ((UINT)STORE_LISP_IN_VOID (Qunbound))
                                intptr_t

dialog-msw.c:764:9: warning: passing argument 4 of 'qxeCreateDialogIndirectParam' from incompatible pointer type [enabled by default]
         (LPARAM) STORE_LISP_IN_VOID (obj));
         ^
          intptr_t

toolbar-msw.c: In function 'mswindows_clear_toolbar':
toolbar-msw.c:100:55: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
       qxeSendMessage (toolbarwnd, TB_GETIMAGELIST, 0, (LONG) &ilist);
                                                       ^
                                                       intptr_t
toolbar-msw.c: In function 'mswindows_output_toolbar':
toolbar-msw.c:370:10: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
          (HMENU)(TOOLBAR_ID_BIAS + pos),
          ^
                 (intptr_t)
In file included from mule-coding.c:32:0:
mule-coding.c: In function 'parse_charset_conversion_specs':

win32.c: In function 'mswindows_lisp_error_1':
win32.c:259:9: warning: format '%ld' expects argument of type 'long int', but argument 3 has type 'DWORD' [-Wformat=]
         errnum, GetLastError ());
         ^
                (long)
win32.c: In function 'Fmswindows_shell_execute':
win32.c:352:11: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
     ret = (int) qxeShellExecute (NULL, opext, doc, parmext, path,
           ^
           intptr-t
win32.c: In function 'setitimer_helper':
win32.c:847:7: warning: passing argument 3 of 'timeSetEvent' from incompatible pointer type [enabled by default]
       event_type);
       ^
 resoluion: pblm is elsewhere?
  setitimer_helper_proc (UINT UNUSED (uID), UINT UNUSED (uMsg), DWORD[_PTR] dwUser,
		       DWORD[_PTR] UNUSED (dw1), DWORD[_PTR] UNUSED (dw2))

> make clean, try again

/usr/local/src/xemacs-21.5-64bit/lib-src/winclient.c: In function 'doFile':
/usr/local/src/xemacs-21.5-64bit/lib-src/winclient.c:299:4: warning: pointer targ
ets in passing argument 1 of 'DdeClientTransaction' differ in signedness [-Wpoint
er-sign]
    0, XTYP_EXECUTE, TRANSACTION_TIMEOUT, NULL);
    ^
In file included from /usr/local/src/xemacs-21.5-64bit/lib-src/winclient.c:27:0:
/usr/include/w32api/ddeml.h:208:19: note: expected 'LPBYTE' but argument is of ty
pe 'char *'
   HDDEDATA WINAPI DdeClientTransaction(LPBYTE pData,DWORD cbData,HCONV hConv,HSZ
 hszItem,UINT wFmt,UINT wType,DWORD dwTimeout,LPDWORD pdwResult);
                   ^
 [note it's arg1 that's the problem, cast to LPBYTE]

event-msw.c:4200:6: warning: passing argument 4 of 'map_event_chain_remove' makes pointer from integer without a cast [enabled by default]
      (intptr_t)id, MECR_DEALLOCATE_EVENT);
      ^
In file included from event-msw.c:72:0:
events.h:956:5: note: expected 'void *' but argument is of type 'long int'
 int map_event_chain_remove (int (*fn) (Lisp_Object ev, void *user_data),
 resolution: hack, but cast _again_, i.e. (void *)(intptr_t)

dialog-msw.c:764:9: warning: passing argument 4 of 'qxeCreateDialogIndirectParam' from incompatible pointer type [enabled by default]
         (intptr_t) STORE_LISP_IN_VOID (obj));
         ^
In file included from syswindows.h:642:0,
                 from console-msw.h:39,
                 from console-msw-impl.h:37,
                 from dialog-msw.c:37:
intl-auto-encap-win32.h:627:6: note: expected 'DLGPROC' but argument is of type 'BOOL (*)(struct HWND__ *, UINT,  WPARAM,  LPARAM)'
 HWND qxeCreateDialogIndirectParam (HINSTANCE hInstance, LPCDLGTEMPLATEW lpTemplate, HWND hWndParent, DLGPROC lpDialogFunc, LPARAM dwInitParam);
 resolved by adding a cast: (DLGPROC)dialog_proc, but not at all sure
that's right

> make clean, try again

intl-win32.c:1509:27: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
     TranslateCharsetInfo ((DWORD *) (DWORD) old_logfont.lfCharSet, &info,
                           ^
 resolution: do nothing -- I think this is necessary because of
             extremely aggressive argument overloading by MS

intl-auto-encap-win32.c:126:5: warning: passing argument 1 of 'ShellExecuteExA' from incompatible pointer type [enabled by default]
     return ShellExecuteExA (pExecInfo);
     ^
In file included from syswindows.h:220:0,
                 from intl-auto-encap-win32.c:12:
/usr/include/w32api/shellapi.h:345:22: note: expected 'struct SHELLEXECUTEINFOA *' but argument is of type 'struct SHELLEXECUTEINFOW *'
   SHSTDAPI_(WINBOOL) ShellExecuteExA (SHELLEXECUTEINFOA *pExecInfo);
                      ^
 resolution: ignored, never used, removed from intl-encap-win32.c

intl-auto-encap-win32.c: In function 'qxeFreeEnvironmentStrings':
intl-auto-encap-win32.c:1771:5: warning: passing argument 1 of 'FreeEnvironmentStringsA' from incompatible pointer type [enabled by default]
     return FreeEnvironmentStringsA (penv);
     ^
In file included from /usr/include/w32api/winbase.h:28:0,
                 from /usr/include/w32api/windows.h:70,
                 from syswindows.h:204,
                 from intl-auto-encap-win32.c:12:
/usr/include/w32api/processenv.h:29:29: note: expected 'LPCH' but argument is of type 'LPWCH'
   WINBASEAPI WINBOOL WINAPI FreeEnvironmentStringsA (LPCH penv);
                             ^
intl-encap-win32.c: In function 'qxeUpdateICMRegKey':
intl-encap-win32.c:1426:36: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
     return UpdateICMRegKeyW (arg1, (DWORD) arg2, (LPWSTR) arg3, arg4);
                                    ^
intl-encap-win32.c:1426:5: warning: passing argument 2 of 'UpdateICMRegKeyW' makes pointer from integer without a cast [enabled by default]
     return UpdateICMRegKeyW (arg1, (DWORD) arg2, (LPWSTR) arg3, arg4);
     ^
In file included from /usr/include/w32api/windows.h:71:0,
                 from syswindows.h:204,
                 from console-msw.h:39,
                 from intl-encap-win32.c:44:
/usr/include/w32api/wingdi.h:3425:28: note: expected 'LPWSTR' but argument is of type 'unsigned int'
   WINGDIAPI WINBOOL WINAPI UpdateICMRegKeyW(DWORD reserved,LPWSTR lpszCMID,LPWSTR lpszFileName,UINT command);
 resolution: nothing, known problem

Similarly wrt qxeEnumResourceTypes, qxeEnumResourceNames,
qxeEnumResourceLanguages, qxeImmSetCompositionString

---------
make clean, recompile, all looks OK, try to track down the problem --
the error in event-msw.c inside mswindow_find_frame, inside
intercepted_wnd_proc (a signal handler?),
where we have a
window with no frame saved, appears to happen when the main thread is
in mswindows_init_frame_1 at frame-msw.c:139
   at recompute_all_cached_specifiers_in_frame at specifier.c:3483
   at recompute_one_cached_specifier_in_frame at specifier.c:3444
    around the sixth one
---
April 2014 above here
----
After a tiny spark on interest on xemacs-beta, did pull -u, merge and
commit, make distclean, configure '--with-pdump=yes' '--with-modules=no' '--with-mule=yes' '--with-ncurses=yes' '--with-msw=yes' '--without-png' '--without-xpm' '--without-jpeg' '--with-cflags-debugging=-ggdb'

No change -- -nw works, w/o -nw gives the same assertion failed.
-----
Trying again, make distclean followed by 
 > 
didn't work!, had to add --without-x (why???)
------
Force debug printing on by
  debug_mswindows_events = 3;
at the end of event-msw.c
Added more printing, removed frame printing, from
debug_output_mswin_message ditto
Narrowed it down to the
   qxeSetWindowLong (hwnd, XWL_FRAMEOBJ, (intptr_t)STORE_LISP_IN_VOID (frame_obj));
at the end of mswindows_init_frame_1 in frame-msw.c
a) Should be ...LongtPtr
b) Not enough room allocated for a 64-bit long ptr -- fixed in
   console-msw-impl.h
----
Trying to get a clean diff to send to Vin
Need Change log entries!
Working with /c/C32/usr/local/src/xemacs-21.5-mine vs. -upstream (now
pulled from xemacs, not xemacs-beta)
_Only_ new files are 
 src/s/cygwin64.h
 src/m/x86_64.h
Changed files are
  > diff -rq --exclude=.hg --exclude=info --exclude=*.{o,i,exe,elc} xemacs-21.5-{upstream,mine}|egrep -v Only | cut -f 2 -d ' ' | cut -f 2- -d /
 ChangeLog
 README
 configure
 configure.ac
 lib-src/gnuclient.c
 lib-src/make-mswin-unicode.pl
 lib-src/winclient.c
 src/console-msw-impl.h
 src/console-msw.c
 src/device-impl.h
 src/device.c
 src/dialog-msw.c
 src/event-msw.c
 src/frame-msw.c
 src/frame.c
 src/glyphs-msw.c
 src/glyphs.c
 src/intl-auto-encap-win32.c
 src/intl-auto-encap-win32.h
 src/intl-encap-win32.c
 src/menubar-msw.c
 src/process-unix.c
 src/scrollbar-msw.c
 src/specifier.c
 src/toolbar-msw.c
 src/win32.c
This version works with cygwin, is in /usr/local/bin as of 28 July.
Subsequent edits are pbly abandoned rework of the cygwin/cygwin32/cygwin64 switch