DWARF: Emit DWARF5 forms for indirect addresses and string offsets.

DWARF: Emit DWARF5 forms for indirect addresses and string offsets.

We already emit DWARF5 attributes and tables for indirect addresses
and string offsets, but still use GNU forms. Add a new helper function
dwarf_FORM () for emitting the right form.

Currently we only use the uleb128 forms. But DWARF5 also allows
1, 2, 3 and 4 byte forms (DW_FORM_strx[1234] and DW_FORM_addrx[1234])
which might be more space efficient.

gcc/ChangeLog

	* dwarf2out.c (dwarf_FORM): New function.
	(set_indirect_string): Use dwarf_FORM.
	(reset_indirect_string): Likewise.
	(size_of_die): Likewise.
	(value_format): Likewise.
	(output_die): Likewise.
	(add_skeleton_AT_string): Likewise.
	(output_macinfo_op): Likewise.
	(index_string): Likewise.
	(output_index_string_offset): Likewise.
	(output_index_string): Likewise.

From-SVN: r260297