[Patch] Fix incorrect code page when setting console title on Win10

[宫大汉]

When Cygwin sets console titles on Win10 (has_con_24bit_colors && !con_is_legacy),
`WriteConsoleA` is used and causes an error if:
1. the environment variable of `LANG` is `***.UTF-8`
2. and the code page of console.exe is not UTF-8
  1. e.g. on my Computer, it's GB2312, for Chinese text


I've done some tests on msys2 and details are on https://github.com/git-for-windows/git/issues/2738,
and I filed a PR of https://github.com/git-for-windows/msys2-runtime/pull/25.
Then what should I do, in order to fix this on Cygwin?


The below is the commit's .patch file:


From 334f52a53a2e6b7f560b0e8810b9f672ebb3ad24 Mon Sep 17 00:00:00 2001
From: Dahan Gong <gdh1995@qq.com>
Date: Fri, 31 Jul 2020 22:06:54 +0800
Subject: [PATCH] Fix incorrect code page in console title


`WriteConsoleA` always follows the current code page of a console window, so it's not suitable to pass a multi-byte string in `get_ttyp ()->term_code_page` to it directly.


This PR turns to `WriteConsoleW` so that most characters will be translated "as is", and I've tested it on Win 10 v2004 (CMD: ver 10.0.19041.388).


Signed-off-by: gdh1995 <gdh1995@qq.com>
---
 winsup/cygwin/fhandler_console.cc | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)


diff --git a/winsup/cygwin/fhandler_console.cc b/winsup/cygwin/fhandler_console.cc
index dd979fb8e2..7870eeda81 100644
--- a/winsup/cygwin/fhandler_console.cc
+++ b/winsup/cygwin/fhandler_console.cc
@@ -80,6 +80,15 @@ static class write_pending_buffer
   {
     WriteConsoleA (handle, buf, ixput, wn, 0);
   }
+  inline char *c_str (size_t *psize = NULL)
+  {
+    size_t size = ixput < WPBUF_LEN ? ixput : WPBUF_LEN - 1;
+    buf[size] = '\0';
+    if (psize != NULL) {
+      *psize = size;
+    }
+    return (char *) buf;
+  }
 } wpbuf;
 
 static void
@@ -3203,7 +3212,14 @@ fhandler_console::write (const void *vsrc, size_t len)
 	    if (*src < ' ')
 	      {
 		if (wincap.has_con_24bit_colors () && !con_is_legacy)
-		  wpbuf.send (get_output_handle ());
+		  {
+		    size_t nms;
+		    char *ms = wpbuf.c_str(&nms);
+		    wchar_t write_buf[TITLESIZE + 1];
+		    DWORD done;
+		    DWORD buf_len = sys_mbstowcs (write_buf, TITLESIZE, ms);
+		    write_console (write_buf, buf_len, done);
+		  }
 		else if (*src == '\007' && con.state == gettitle)
 		  set_console_title (con.my_title_buf);
 		con.state = normal;