PR middle-end/42859

    * tree-eh.c: Include pointer-set.h.
    (lower_eh_dispatch): Filter out duplicate case labels and
    remove the unneeded edge when the label is unused.  Return
    true when some edges are removed.
    (execute_lower_eh_dispatch): When any lowering resulted in
    removing an edge, also delete unreachable blocks.

    * g++.dg/eh/pr42859.C: New test.

From-SVN: r157337