Have pg_upgrade only use one extra log file for Win32, not two.

contrib/pg_upgrade/pg_upgrade.c

@@ -58,8 +58,8 @@ OSInfo		os_info;
 char *output_files[] = {
 	SERVER_LOG_FILE,
 #ifdef WIN32
+	/* unique file for pg_ctl start */
 	SERVER_START_LOG_FILE,
-	SERVER_STOP_LOG_FILE,
 #endif
 	RESTORE_LOG_FILE,
 	UTILITY_LOG_FILE,

contrib/pg_upgrade/pg_upgrade.h

@@ -63,7 +63,8 @@ extern char *output_files[];
 #define SERVER_STOP_LOG_FILE	SERVER_LOG_FILE
 #else
 #define SERVER_START_LOG_FILE	"pg_upgrade_server_start.log"
-#define SERVER_STOP_LOG_FILE	"pg_upgrade_server_stop.log"
+/* pg_ctl stop doesn't keep the log file open, so reuse UTILITY_LOG_FILE */
+#define SERVER_STOP_LOG_FILE	UTILITY_LOG_FILE
 #endif