gcov: Add gen_counter_update()
Move the counter update to the new gen_counter_update() helper function. Use
it in gimple_gen_edge_profiler() and gimple_gen_time_profiler(). The resulting
gimple instructions should be identical with the exception of the removed
unshare_expr() call. The unshare_expr() call was used in
gimple_gen_edge_profiler().
gcc/ChangeLog:
* tree-profile.cc (gen_assign_counter_update): New.
(gen_counter_update): Likewise.
(gimple_gen_edge_profiler): Use gen_counter_update().
(gimple_gen_time_profiler): Likewise.