patch 8.2.5077: various warnings from clang on MS-Windows

Problem:    Various warnings from clang on MS-Windows.
Solution:   Avoid the warnings. (Yegappan Lakshmanan, closes #10553)

src/os_win32.c

@@ -2355,11 +2355,11 @@ theend:
  * worth allowing these to make debugging of issues easier.
  */
     static void
-bad_param_handler(const wchar_t *expression,
-    const wchar_t *function,
-    const wchar_t *file,
-    unsigned int line,
-    uintptr_t pReserved)
+bad_param_handler(const wchar_t *expression UNUSED,
+    const wchar_t *function UNUSED,
+    const wchar_t *file UNUSED,
+    unsigned int line UNUSED,
+    uintptr_t pReserved UNUSED)
 {
 }