pg_ctl: Sort signal list in --help output

The list was neither logical nor numerical nor alphabetical.  Let's go
with alphabetical.

src/bin/pg_ctl/pg_ctl.c

@@ -1791,7 +1791,7 @@ do_help(void)
 	printf(_("  immediate   quit without complete shutdown; will lead to recovery on restart\n"));
 
 	printf(_("\nAllowed signal names for kill:\n"));
-	printf("  HUP INT QUIT ABRT TERM USR1 USR2\n");
+	printf("  ABRT HUP INT QUIT TERM USR1 USR2\n");
 
 #if defined(WIN32) || defined(__CYGWIN__)
 	printf(_("\nOptions for register and unregister:\n"));