util/set: Add specialized resizing add function

util/set: Add specialized resizing add function

A significant portion of the time spent in nir_opt_cse for the Dolphin
ubershaders was in resizing the set. When resizing a hash table, we know
in advance that each new element to be inserted will be different from
every other element, so we don't have to compare them, and there will be
no tombstone elements, so we don't have to worry about caching the
first-seen tombstone. We add a specialized add function which skips
these steps entirely, speeding up resizing.

Compile-time results from my shader-db database:

Difference at 95.0% confidence
	-2.29143 +/- 0.845534
	-0.529475% +/- 0.194767%
	(Student's t, pooled s = 1.08807)

Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>