patch 8.1.2064: MS-Windows: compiler warnings for unused arguments

Problem:    MS-Windows: compiler warnings for unused arguments.
Solution:   Add UNUSED. (Yegappan Lakshmanan, closes #4963)
diff --git a/src/terminal.c b/src/terminal.c
index 3d66bbb..a8b7881 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -957,7 +957,7 @@
  * possible to do "1,5term vim -".
  */
     static ch_part_T
-get_tty_part(term_T *term)
+get_tty_part(term_T *term UNUSED)
 {
 #ifdef UNIX
     ch_part_T	parts[3] = {PART_IN, PART_OUT, PART_ERR};
@@ -5787,7 +5787,7 @@
 conpty_term_and_job_init(
 	term_T	    *term,
 	typval_T    *argvar,
-	char	    **argv,
+	char	    **argv UNUSED,
 	jobopt_T    *opt,
 	jobopt_T    *orig_opt)
 {
@@ -6139,7 +6139,7 @@
 winpty_term_and_job_init(
 	term_T	    *term,
 	typval_T    *argvar,
-	char	    **argv,
+	char	    **argv UNUSED,
 	jobopt_T    *opt,
 	jobopt_T    *orig_opt)
 {