[PATCH] Speed up IMA and mergedecls

[Andrew Pinski <pinskia at physics dot uc dot edu>]

Even though we are into stage3, I am going to send this because it
makes --enable-intermodule usable and IMA even more.  I can now build
GCC in a more reasonable time with --enable-intermodule with this patch.
Basically we can cache more if two types have been considered
compatible and also keep it over the whole comptypes.  Also now most of
the time is spent in the tree optimizers rather than the front-end.

OK? Bootstrapped and tested on powerpc-darwin with no regressions.

ChangeLog:
	* c-typeck.c (comptypes): Move functional to comptypes_internal
	and free tagged_tu_seen.
	(comptypes_internal): New function and call comptypes_internal
	instead of comptypes.
	(alloc_tagged_tu_seen): New function
	(free_all_tagged_tu_seen_up_to): New function.
	(tagged_types_tu_compatible_p): Add that the two types are the
	same to tagged_tu_seen_base if they are and call comptypes_internal
	instead of comptypes.
	<case UNION_TYPE>: Speed up common type where the fields are
	in the same order.
	(function_types_compatible_p): Call comptypes_internal instead of
	comptypes.
	(type_lists_compatible_p): Likewise.

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