tests: select V1 for empty struct C output

Author: medvednikov

vlib/v/gen/c/empty_struct_default_codegen_test.v

@@ -12,7 +12,7 @@ fn test_empty_struct_defaults_use_msvc_compatible_initializer() {
 	os.write_file(source_path,
 		'import x.json2\n\n__global empty json2.Null\n\nfn main() {\n\tparsed := json2.decode[json2.Any](\'{"a":1}\') or { return }\n\tprintln(parsed)\n\tprintln(empty)\n}\n')!
 	result :=
-		os.execute('${empty_struct_default_vexe} -enable-globals -o - ${os.quoted_path(source_path)}')
+		os.execute('${empty_struct_default_vexe} -old-compiler -enable-globals -o - ${os.quoted_path(source_path)}')
 	assert result.exit_code == 0, result.output
 	assert result.output.contains('(json2__Null){E_STRUCT}'), result.output
 	assert !result.output.contains('(json2__Null){}'), result.output