loc_list_for_tree_1 and add_const_value_attribute currently ICE
on POLY_INTs.  loc_list_for_tree_1 can do something sensible but
add_const_value_attribute has to punt, since the constant there
needs to be a link-time rather than load-time or run-time constant.

This is tested by later SVE patches.

2019-09-18  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* dwarf2out.c (loc_list_from_tree_1): Handle POLY_INT_CST.
	(add_const_value_attribute): Handle CONST_POLY_INT.

From-SVN: r275868