MinGW build broken with O_CLOEXEC undeclared

[martin rudalics <rudalics@gmx.at>]

Compiling master is currently broken on my Windows XP (MinGW gcc 4.8.1) as below

../../lib/futimens.c:31:1: warning: no previous prototype for 'futimens' [-Wmissing-prototypes]
  futimens (int fd, struct timespec const times[2])
  ^
   CC       getopt1.o
   CC       gettimeofday.o
   CC       memmem.o
   CC       mempcpy.o
   CC       memrchr.o
   CC       mkostemp.o
   CC       mktime.o
   CC       open.o
../../lib/open.c: In function 'sys_open':
../../lib/open.c:127:49: error: 'O_CLOEXEC' undeclared (first use in this function)
                    flags & ~(have_cloexec <= 0 ? O_CLOEXEC : 0), mode);
                                                  ^
../../lib/open.c:127:49: note: each undeclared identifier is reported only once for each function it appears in
make[1]: *** [open.o] Error 1
make[1]: *** Waiting for unfinished jobs....
make[1]: Leaving directory `/c/emacs-git/trunk/dbg/lib'
make: *** [lib] Error 2

martin