Support namespaces in DWARF 2 output.

Support namespaces in DWARF 2 output.

        * dwarf2out.c (gen_namespace_die): New function.
        (force_namespace_die, setup_namespace_context): New fns.
        (declare_in_namespace): New fn.
        (gen_decl_die): Call declare_in_namespace.  Handle namespaces.
        (dwarf2out_decl): Handle namespaces.
        (scope_die_for): Pass through a namespace scope.
        (class_scope_p): Rename to class_or_namespace_scope_p.
        (gen_subprogram_die, gen_variable_die): Adjust.
        (gen_struct_or_union_die): Always emit a declaration
        if context_die is a namespace.

Co-Authored-By: Daniel Berlin <dberlin@dberlin.org>
From-SVN: r74436