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/modules/fcntl
+++ b/modules/fcntl
@@ -1,11 +1,12 @@
 Description:
-Support for fcntl() action F_DUPFD_CLOEXEC.
+Support for fcntl() action F_DUPFD, F_DUPFD_CLOEXEC, F_GETFD.
 
 Files:
 m4/fcntl.m4
 lib/fcntl.c
 
 Depends-on:
+dup2
 fcntl-h
 
 configure.ac: