runtime(doc): clarify temporary file clean up

related: #14770

Co-authored-by: Enno <Konfekt@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/builtin.txt

@@ -1,4 +1,4 @@
-*builtin.txt*	For Vim version 9.1.  Last change: 2024 May 15
+*builtin.txt*	For Vim version 9.1.  Last change: 2024 May 18
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -10243,7 +10243,9 @@ tempname()					*tempname()* *temp-file-name*
 		is different for at least 26 consecutive calls.  Example: >
 			:let tmpfile = tempname()
 			:exe "redir > " .. tmpfile
-<		For Unix, the file will be in a private directory |tempfile|.
+<		For Unix, the file will be in a private directory |tempfile|
+		that is recursively deleted when Vim exits, on other systems
+		temporary files are not cleaned up automatically on exit.
 		For MS-Windows forward slashes are used when the 'shellslash'
 		option is set, or when 'shellcmdflag' starts with '-' and
 		'shell' does not contain powershell or pwsh.

runtime/doc/change.txt

@@ -1,4 +1,4 @@
-*change.txt*    For Vim version 9.1.  Last change: 2024 May 05
+*change.txt*    For Vim version 9.1.  Last change: 2024 May 18
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -623,7 +623,8 @@ Vim uses temporary files for filtering, generating diffs and also for
 tempname().  For Unix, the file will be in a private directory (only
 accessible by the current user) to avoid security problems (e.g., a symlink
 attack or other people reading your file).  When Vim exits the directory and
-all files in it are deleted.  When Vim has the setuid bit set this may cause
+all files in it are deleted (only on Unix, on other systems you will have to
+clean up yourself).  When Vim has the setuid bit set this may cause
 problems, the temp file is owned by the setuid user but the filter command
 probably runs as the original user.
 Directory for temporary files is created in the first of these directories