Minor type merging optimization

[Jan Hubicka]

> I haven't yet tested this (apart from with running the LTO testsuite),
> but I'm going to give the following bootstrap & SPEC2k6 LTO build tests.
> 
> Richard.
> 
> 2011-05-09  Richard Guenther  <rguenther@suse.de>
> 
> 	* gimple.c (gtc_visited, gtc_ob, struct type_pair_d, type_pair_t,
> 	type_pair_hash, type_pair_eq, lookup_type_pair): Remove.
> 	(gtc_visit): Adjust.  Use the first type to identify the
> 	part of the SCC we are visiting.
> 	(gimple_types_compatible_p_1): Likewise.
> 	(gimple_types_compatible_p): Likewise.
> 	(print_gimple_types_stats): Do not print comparison cache stats.
> 	(free_gimple_type_tables): Do not free the comparison cache.

Thanks,
I will benchmark Mozilla now.
Honza