sort,split,yes: ensure pipe and pipe2 don't open standard descriptors

* bootstrap.conf (gnulib_modules): Add pipe2-safer.
* cfg.mk (sc_require_unistd_safer): New rule for 'make syntax-check'.
* gl/lib/fd-reopen.c: Include unistd--.h instead of unistd.h.
* src/sort.c: Include unistd--.h.
* src/split.c: Likewise.
* src/yes.c: Likewise.

bootstrap.conf

@@ -213,6 +213,7 @@ gnulib_modules="
   physmem
   pipe-posix
   pipe2
+  pipe2-safer
   posix-shell
   posix_spawn
   posix_spawn_file_actions_addclose

cfg.mk

@@ -603,6 +603,19 @@ sc_require_stdlib_safer:
 	else :;								\
 	fi
 
+# Ensure that "unistd--.h" is used where appropriate.
+sc_require_unistd_safer:
+	@if $(VC_LIST_EXCEPT) | grep -l '\.[ch]$$' > /dev/null; then	\
+	  files=$$(grep -El '$(begword)(pipe2?|dup[23]?) ?\('		\
+		   $$($(VC_LIST_EXCEPT)					\
+	      | grep '\.[ch]$$'));					\
+	  test -n "$$files" && grep -LE 'include "unistd--.h"' $$files	\
+	      | grep . &&						\
+	  { echo '$(ME): the above files should use "unistd--.h"'	\
+		1>&2; exit 1; } || :;					\
+	else :;								\
+	fi
+
 sc_prohibit_perl_hash_quotes:
 	@prohibit="\{'[A-Z_]+' *[=}]"					\
 	halt="in Perl code, write \$$hash{KEY}, not \$$hash{'K''EY'}"	\

gl/lib/fd-reopen.c

@@ -23,7 +23,7 @@
 
 #include <errno.h>
 #include <fcntl.h>
-#include <unistd.h>
+#include "unistd--.h"
 
 /* Open a file to a particular file descriptor.  This is like standard
    'open', except it always returns DESIRED_FD if successful.  */

src/sort.c

@@ -51,6 +51,7 @@
 #include "stdlib--.h"
 #include "strnumcmp.h"
 #include "term-sig.h"
+#include "unistd--.h"
 #include "xmemcoll.h"
 #include "xnanosleep.h"
 #include "xstrtol.h"

src/split.c

@@ -40,6 +40,7 @@
 #include "sig2str.h"
 #include "sys-limits.h"
 #include "temp-stream.h"
+#include "unistd--.h"
 #include "xbinary-io.h"
 #include "xdectoint.h"
 #include "xstrtol.h"

src/yes.c

@@ -27,6 +27,7 @@
 #include "full-write.h"
 #include "isapipe.h"
 #include "long-options.h"
+#include "unistd--.h"
 
 /* The official name of this program (e.g., no 'g' prefix).  */
 #define PROGRAM_NAME "yes"