glsl: Don't hide the type of struct_declaration_list.

I've been trying to derive from this for UBO support, and the slightly
obfuscated types were putting me over the edge.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/ast.h

@@ -417,15 +417,19 @@ struct ast_type_qualifier {
    const char *interpolation_string() const;
 };
 
+class ast_declarator_list;
+
 class ast_struct_specifier : public ast_node {
 public:
-   ast_struct_specifier(const char *identifier, ast_node *declarator_list);
+   ast_struct_specifier(const char *identifier,
+			ast_declarator_list *declarator_list);
    virtual void print(void) const;
 
    virtual ir_rvalue *hir(exec_list *instructions,
 			  struct _mesa_glsl_parse_state *state);
 
    const char *name;
+   /* List of ast_declarator_list * */
    exec_list declarations;
 };