[PATCH]: Clear SSA_NAME_DEF_STMT on released SSA names

[Daniel Berlin]

> Bad idea unless something has changed.
>
> SSA_NAME_DEF_STMT uses the tree chain field.  WHen we release an
> SSA_NAME we use the chain field to link together all the free SSA_NAME
> nodes.

Interesting. It survived bootstrap and regtesting here.
It must be reset later on again to chain them together.

>
> jeff
>
>