patch 9.1.1727: Nextstep support still included

Problem:  Nextstep support still included
Solution: Deprecate Nextstep code and undef corresponding feature flag

closes: #18131

Signed-off-by: Damien Lejay <damien@lejay.be>
Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: dlejay

runtime/doc/vi_diff.txt

@@ -1,4 +1,4 @@
-*vi_diff.txt*   For Vim version 9.1.  Last change: 2025 Aug 10
+*vi_diff.txt*   For Vim version 9.1.  Last change: 2025 Sep 02
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1398,5 +1398,6 @@ MS-DOS:				| support was dropped with v7.4.1399
 MS-Windows XP and Vista:	| support was dropped with v9.0.0496
 OS/2				| support was dropped with v7.4.1008
 RISC OS:			| support was dropped with v7.3.0187
+NextStep Systems		| support was deprecated with v9.1.1727
 
  vim:tw=78:ts=8:noet:ft=help:norl:

src/version.c

@@ -724,6 +724,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1727,
 /**/
     1726,
 /**/

src/vim.h

@@ -40,6 +40,22 @@
 #  error configure did not run properly.  Check auto/config.log.
 # endif
 
+/*
+ * NeXTSTEP / OPENSTEP support deprecation
+ *
+ * NeXT hardware was discontinued in 1993, and the last OPENSTEP release
+ * (4.2) shipped in 1996–1997. No known users remain today.
+ *
+ * To simplify maintenance, NeXT support is formally deprecated. If you hit
+ * this error, please report it to the Vim maintainers.
+ *
+ * This guard will be removed once the remaining NeXT-specific code paths
+ * are deleted in a future release.
+ */
+#if defined(NeXT) || defined(__NeXT__)
+# error "NeXTSTEP / OPENSTEP support has been deprecated."
+#endif
+
 # if (defined(__linux__) && !defined(__ANDROID__)) || defined(__CYGWIN__) || defined(__GNU__)
 // Needed for strptime().  Needs to be done early, since header files can
 // include other header files and end up including time.h, where these symbols