Windows mingw64 and cygwin builds broken

[Andy Moreton <andrewjmoreton@gmail.com>]

Hi,

Changes in commit 9d43941569fc broke the Windows builds.

1) Mingw64 (64bit, msys2 hosted)

The mingw64 failures appear to be caused by using the
NOTIFYICONDATAW_V3_SIZE  macro from the mingw64 shellapi.h header,
which depends on the build-time definition of NTDDI_VERSION.

--[msys2 mingw64 64bit]-----------------------------------------------
In file included from C:/msys64/mingw64/x86_64-w64-mingw32/include/minwindef.h:163:0,
                 from C:/msys64/mingw64/x86_64-w64-mingw32/include/windef.h:8,
                 from C:/msys64/mingw64/x86_64-w64-mingw32/include/windows.h:69,
                 from ../../src/w32gui.h:21,
                 from ../../src/w32term.h:21,
                 from ../../src/w32fns.c:35:
../../src/w32fns.c: In function 'add_tray_notification':
../../src/w32fns.c:8904:16: error: 'NOTIFYICONDATAW {aka struct _NOTIFYICONDATAW}' has no member named 'hBalloonIcon'
  nidw.cbSize = NOTIFYICONDATAW_V3_SIZE;
                ^
Makefile:364: recipe for target 'w32fns.o' failed
--[msys2 mingw64 64bit]-----------------------------------------------


2) Cygwin w32 build (64bit)

The cygwin w32 build breaks because it builds w32fns.c but uses
different filename manipulation routines:

--[cygwin-w32]--------------------------------------------------------
In file included from /usr/include/w32api/minwindef.h:163:0,
                 from /usr/include/w32api/windef.h:8,
                 from /usr/include/w32api/windows.h:69,
                 from /cygdrive/c/emacs/git/emacs/master/src/w32gui.h:21,
                 from /cygdrive/c/emacs/git/emacs/master/src/w32term.h:21,
                 from /cygdrive/c/emacs/git/emacs/master/src/w32fns.c:35:
/cygdrive/c/emacs/git/emacs/master/src/w32fns.c: In function ‘add_tray_notification’:
/cygdrive/c/emacs/git/emacs/master/src/w32fns.c:8904:16: error: ‘NOTIFYICONDATAW’ has no member named ‘hBalloonIcon’
  nidw.cbSize = NOTIFYICONDATAW_V3_SIZE;
                ^
/cygdrive/c/emacs/git/emacs/master/src/w32fns.c:8921:8: warning: implicit declaration of function ‘filename_to_utf16’ [-Wimplicit-function-declaration]
        if (filename_to_utf16 (icon, icon_w) != 0)
        ^
/cygdrive/c/emacs/git/emacs/master/src/w32fns.c:8933:8: warning: implicit declaration of function ‘filename_to_ansi’ [-Wimplicit-function-declaration]
        if (filename_to_ansi (icon, icon_a) != 0)
        ^
/cygdrive/c/emacs/git/emacs/master/src/w32fns.c:8960:4: warning: implicit declaration of function ‘pMultiByteToWideChar’ [-Wimplicit-function-declaration]
    tiplen = pMultiByteToWideChar (CP_UTF8, MB_ERR_INVALID_CHARS,
    ^
Makefile:364: recipe for target 'w32fns.o' failed
--[cygwin-w32]--------------------------------------------------------