patch 9.1.0908: not possible to configure :messages

Problem:  not possible to configure :messages
Solution: add the 'messagesopt' option (Shougo Matsushita)

closes: #16068

Co-authored-by: h_east <h.east.727@gmail.com>
Signed-off-by: Shougo Matsushita <Shougo.Matsu@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/optwin.vim b/runtime/optwin.vim
index c8170da..c3f917c 100644
--- a/runtime/optwin.vim
+++ b/runtime/optwin.vim
@@ -749,8 +749,8 @@
 call <SID>BinOptionG("terse", &terse)
 call <SID>AddOption("shortmess", gettext("list of flags to make messages shorter"))
 call <SID>OptionG("shm", &shm)
-call <SID>AddOption("msghistory", gettext("how many messages are remembered"))
-call append("$", " \tset mhi=" . &mhi)
+call <SID>AddOption("messagesopt", gettext("Option settings when outputting messages"))
+call <SID>OptionG("mopt", &mopt)
 call <SID>AddOption("showcmd", gettext("show (partial) command keys in location given by 'showcmdloc'"))
 let &sc = s:old_sc
 call <SID>BinOptionG("sc", &sc)