Remove shadowed oracle field.

Remove shadowed oracle field.

The m_oracle field in the path solver was shadowing the base class.
This was causing subtle problems while calculating outgoing edges
between blocks, because the query object being passed did not have an
oracle set.

This should further improve our solving ability.

Tested on x86-64 Linux.

gcc/ChangeLog:

	* gimple-range-path.cc (path_range_query::compute_ranges): Use
	get_path_oracle.
	* gimple-range-path.h (class path_range_query): Remove shadowed
	m_oracle field.
	(path_range_query::get_path_oracle): New.