[newlib-cygwin] Cygwin: describe new locale modifier @cjksingle for user guide

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=b7361d31fb8659aa6cea85d7eef22471727be26b

commit b7361d31fb8659aa6cea85d7eef22471727be26b
Author: Thomas Wolff <mintty@users.noreply.github.com>
Date:   Mon Feb 17 00:00:00 2020 +0100

    Cygwin: describe new locale modifier @cjksingle for user guide

Diff:
---
 winsup/doc/setup-locale.xml | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/winsup/doc/setup-locale.xml b/winsup/doc/setup-locale.xml
index 4872ae2..4b9141e 100644
--- a/winsup/doc/setup-locale.xml
+++ b/winsup/doc/setup-locale.xml
@@ -179,6 +179,17 @@ response with this option; it forces wcwidth/wcswidth to return 2 for the
 ambiguous width characters.
 </para></listitem>
 
+<listitem><para>
+As an alternative preference, CJK single-width may be enforced.
+This feature is a
+<ulink url="https://gitlab.freedesktop.org/terminal-wg/specifications/issues/9#note_406682">proposal</ulink>
+in the Terminals Working Group Specifications.
+The mintty terminal implements it as an option with proper glyph scaling.
+The locale modifier "@cjksingle" supports consistent locale response
+with this option; it forces wcwidth/wcswidth to account at most 1 for
+all characters.
+</para></listitem>
+
 </itemizedlist>
 
 </sect2>