Fix type of bitstart in vectorizable_live_operation

Fix type of bitstart in vectorizable_live_operation

This patch changes the type of the multiplier applied by
vectorizable_live_operation from unsigned_type_node to bitsizetype,
which matches the type of TYPE_SIZE and is the type expected of a
BIT_FIELD_REF bit position.  This is shown by existing tests when
SVE is added.

2017-09-18  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree-vect-loop.c (vectorizable_live_operation): Fix type of
	bitstart.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r252931