bug#42095: 28.0.50; Build fails on Windows/MinGW64

[Peder O. Klingenberg]

I wanted to refresh my Windows Emacs build tonight, for the first time
in some months.  I pulled up to
5ce5cf643840cd6efd25d987bc5b6f12478c50a6 by Paul Eggert and ran make -j4
as usual.  The build failed.  Likewise make bootstrap.  The error:

  CC       open.o
open.c: In function 'sys_open':
open.c:127:48: error: 'O_CLOEXEC' undeclared (first use in this function)
  127 |                   flags & ~(have_cloexec < 0 ? O_CLOEXEC : 0), mode);
      |                                                ^~~~~~~~~
open.c:127:48: note: each undeclared identifier is reported only once for each 
function it appears in

That line was changed a few hours ago, in commit
118c07e02e939c9f52688091509d4bff2a897032, also by Paul.

Checking out the commit prior to 118c07 seems to get past the error.
The line and its surroundings look fairly similar in that revision
(ffb89e), so I'm not sure what would be the proper fix.  Hence no
patch, sorry.

...Peder...
-- 
I wish a new life awaited _me_ in some off-world colony.