asn1: don't include decoration header for void *

If the decorated external type is a void *, don't include the decoration
header in the ASN.1 header, only in the template implementation. This allows
the copy constructor and destructor to be implementation private.

lib/asn1/gen.c

@@ -1641,6 +1641,7 @@ declare_type(const Symbol *s, Type *t, int typedefp)
 	getnewbasename(&newbasename, TRUE, s->gen_name, s->gen_name);
 	fprintf(headerfile, "struct %s %s;\n", newbasename, s->gen_name);
         if (decorate_type(newbasename, &deco) && deco.header_name
+	    && !deco.void_star
             && deco.header_name[0]) {
             fprintf(headerfile, "#include %s\n", deco.header_name);
             free(deco.field_type);