fcntl: port portions of fcntl to mingw Borrow ideas from dup_cloexec and dup3 to implement F_DUPFD and F_DUPFD_CLOEXEC. Support querying the inheritance status via F_GETFD, but for now, no support for changing with F_SETFD. The remaining portions of fcntl fail with EINVAL. * m4/fcntl.m4 (gl_FUNC_FCNTL): Also build fcntl.c on mingw. * lib/fcntl.c (fcntl) <F_DUPFD, F_DUPFD_CLOEXEC, F_GETFD>: Provide replacement for mingw. * modules/fcntl (Description): Update. (Depends-on): Add dup2. * m4/fcntl_h.m4 (gl_FCNTL_H_DEFAULTS): Add witness. * modules/fcntl-h (Makefile.am): Substitute it. * lib/fcntl.in.h (fcntl): Update declaration. (F_DUPFD, F_GETFD): New macros, when needed. * doc/posix-headers/fcntl.texi (fcntl.h): Update documentation. * doc/posix-functions/fcntl.texi (fcntl): Likewise. * tests/test-fcntl.c (check_flags, main): Enhance test for items we now guarantee. Signed-off-by: Eric Blake <ebb9@byu.net>

--- a/m4/fcntl_h.m4
+++ b/m4/fcntl_h.m4
@@ -1,4 +1,4 @@
-# serial 7
+# serial 8
 # Configure fcntl.h.
 dnl Copyright (C) 2006, 2007, 2009 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
@@ -101,6 +101,7 @@
   GNULIB_OPEN=0;    AC_SUBST([GNULIB_OPEN])
   GNULIB_OPENAT=0;  AC_SUBST([GNULIB_OPENAT])
   dnl Assume proper GNU behavior unless another module says otherwise.
+  HAVE_FCNTL=1;     AC_SUBST([HAVE_FCNTL])
   HAVE_OPENAT=1;    AC_SUBST([HAVE_OPENAT])
   REPLACE_FCNTL=0;  AC_SUBST([REPLACE_FCNTL])
   REPLACE_OPEN=0;   AC_SUBST([REPLACE_OPEN])