poly_int: get_binfo_at_offset

poly_int: get_binfo_at_offset

This patch changes the offset parameter to get_binfo_at_offset
from HOST_WIDE_INT to poly_int64.  This function probably doesn't
need to handle polynomial offsets in practice, but it's easy
to do and avoids forcing the caller to check first.

2017-12-21  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree.h (get_binfo_at_offset): Take the offset as a poly_int64
	rather than a HOST_WIDE_INT.
	* tree.c (get_binfo_at_offset): Likewise.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r255932