Disambiguate a statement.
(dimb-stmt stmt table) → (mv erp new-stmt new-table)
A compound statement form a new scope. Thus we push a new scope before the block, which we pop after the block.
A selection statement forms a new scope, as do its sub-statements [C:6.8.4/3].
An iteration statement forms a new scope, as do its sub-statements [C:6.8.5/5].