patch 8.1.0879: MS-Windows: temp name encoding can be wrong

Problem:    MS-Windows: temp name encoding can be wrong.
Solution:   Convert from active code page to 'encoding'. (Ken Takata,
            closes #3520, closes #1698)

src/fileio.c

@@ -7470,6 +7470,24 @@ vim_tempname(
 	for (p = retval; *p; ++p)
 	    if (*p == '\\')
 		*p = '/';
+
+#if defined(FEAT_MBYTE) && defined(WIN3264)
+    if (enc_utf8)
+    {
+	int	len;
+	char_u  *pp = NULL;
+
+	// Convert from active codepage to UTF-8 since mch_call_shell()
+	// converts command-line to wide string from encoding.
+	acp_to_enc(retval, (int)STRLEN(retval), &pp, &len);
+	if (pp != NULL)
+	{
+	    vim_free(retval);
+	    return pp;
+	}
+    }
+#endif
+
     return retval;
 
 # else /* WIN3264 */

src/version.c

@@ -783,6 +783,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    879,
 /**/
     878,
 /**/