Fit cell width to content

td {
    border: 1px solid #000;
}

tr td:last-child {
    width: 1%;
    white-space: nowrap;
}

<table style="width: 100%;">
    <tr>
        <td class="block">this should stretch</td>
        <td class="block">this should stretch</td>
        <td class="block">this should be the content width</td>
    </tr>
</table>