Turn var-tracking.c:INT_MEM_OFFSET into a function

Turn var-tracking.c:INT_MEM_OFFSET into a function

This avoids the double evaluation mentioned in the comments and
simplifies the change to make MEM_OFFSET variable.

2017-11-01  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* var-tracking.c (INT_MEM_OFFSET): Replace with...
	(int_mem_offset): ...this new function.
	(var_mem_set, var_mem_delete_and_set, var_mem_delete)
	(find_mem_expr_in_1pdv, dataflow_set_preserve_mem_locs)
	(same_variable_part_p, use_type, add_stores, vt_get_decl_and_offset):
	Update accordingly.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r254309