ada: Fix DWARF for certain arrays

An array whose index type is a nonstandard enum will be marked as
"packed", but should not emit DW_AT_bit_stride unless it is also
bit-packed.

gcc/ada/

	* gcc-interface/decl.cc (gnat_to_gnu_entity): Set bit-packed for
	constrained and unconstrained array types.
	* gcc-interface/misc.cc (gnat_get_array_descr_info): Examine
	BIT_PACKED_ARRAY_TYPE_P.

• [DBH] gcc/ada/gcc-interface/decl.cc
• [DBH] gcc/ada/gcc-interface/misc.cc