Further use of mod_scope in modified_type_die

Further use of mod_scope in modified_type_die

I am working on some changes to GNAT to emit hierarchical DWARF --
i.e., where entities will have simple names nested in a DW_TAG_module.

While working on this I found a couple of paths in modified_type_die
where "mod_scope" should be used, but is not.  I suspect these cases
are only reachable by Ada code, as in both spots (subrange types and
base types), I believe that other languages don't generally have named
types in a non-top-level scope, and in these other situations,
mod_scope will still be correct.

gcc

	* dwarf2out.cc (modified_type_die): Use mod_scope for
	ranged types, base types, and array types.