gi: maybe suppress the following warnings on armv7hl

    rb-gi-function-info.c: In function 'rb_gi_function_info_invoke_raw_call':
    rb-gi-function-info.c:579:32: warning: cast increases required alignment of target type [-Wcast-align]
                                    (GIArgument *)(data->in_args->data),
                                    ^
    rb-gi-function-info.c:581:32: warning: cast increases required alignment of target type [-Wcast-align]
                                    (GIArgument *)(data->out_args->data),
                                    ^

GitHub: #216

Reported by mtaska. Thanks!!!