Add DW_AT_const_value as unsigned or int depending on type and value used.

As the comment in the code already indicated DWARF2 does provide
DW_FORM_sdata/DW_FORM_udata to represent signed/unsigned data.
Enumeration constants wider than HOST_WIDE_INT are already handled
separately. Those constant values that do fit a HOST_WIDE_INT can
be encoded as signed or unsigned depending on type and value for
more efficient encoding.

	* dwarf2out.c (gen_enumeration_type_die): Add DW_AT_const_value
	as unsigned or int depending on type and value used.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@209424 138bc75d-0d04-0410-961f-82ee72b054a4