Fix profile updating bug in tree-ssa-threadupdate

ssa_fix_duplicate_block_edges later calls update_profile to correct profile after threading.
In the testcase this does not work since we lose track of the duplicated edge.  This
happens because redirect_edge_and_branch returns NULL if the edge already has correct
destination which is the case.

gcc/ChangeLog:

	* tree-ssa-threadupdate.cc (ssa_fix_duplicate_block_edges): Fix profile update.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/phi_on_compare-1.c: Check profile consistency.