Fix build of ICU support in Windows

and also any platform that does not have locale_t but enabled ICU.

Author: Ashutosh Sharma <ashu.coek88@gmail.com>

src/backend/commands/collationcmds.c

@@ -411,10 +411,10 @@ get_icu_locale_comment(const char *localename)
 Datum
 pg_import_system_collations(PG_FUNCTION_ARGS)
 {
-#if defined(HAVE_LOCALE_T) && !defined(WIN32)
 	bool		if_not_exists = PG_GETARG_BOOL(0);
 	Oid			nspid = PG_GETARG_OID(1);
 
+#if defined(HAVE_LOCALE_T) && !defined(WIN32)
 	FILE	   *locale_a_handle;
 	char		localebuf[NAMEDATALEN]; /* we assume ASCII so this is fine */
 	int			count = 0;
@@ -431,6 +431,12 @@ pg_import_system_collations(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 				 (errmsg("must be superuser to import system collations"))));
 
+#if !(defined(HAVE_LOCALE_T) && !defined(WIN32)) && !defined(USE_ICU)
+	/* silence compiler warnings */
+	(void) if_not_exists;
+	(void) nspid;
+#endif
+
 #if defined(HAVE_LOCALE_T) && !defined(WIN32)
 	locale_a_handle = OpenPipeStream("locale -a", "r");
 	if (locale_a_handle == NULL)