GC special object sizes

[Steven Bosscher]

Hi,

With Zack's work to make TREE_CST_RTL go away, a bunch of objects are
now only 20 bytes instead of 24, so they go in special page now.  But
there are many more trees of 24 bytes per tree.  All tree_exp trees with
two operands, for example, and there are many of those: 65 in tree.def,
3 more in c-common.def, and another 11 in cp/cp-tree.def.

So why isn't there a special page for objects with a size of 24 bytes?

Greetz
Steven