patch 8.2.3977: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/terminal.c b/src/terminal.c
index ca5b835..d974c11 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -935,7 +935,7 @@
 	vim_snprintf((char *)newcmd, cmdlen, "%s %s %s", p_sh, p_shcf, cmd);
 	cmd = newcmd;
 # else
-	emsg(_("E279: Sorry, ++shell is not supported on this system"));
+	emsg(_(e_sorry_plusplusshell_not_supported_on_this_system));
 	goto theend;
 # endif
 #endif