<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/124947>124947</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc][POSIX] provide _POSIX_ARG_MAX in limits.h
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            good first issue,
            libc
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          nickdesaulniers
      </td>
    </tr>
</table>

<pre>
    building llvm against llvm-libc fails with:
```
/llvm-project-main/llvm/lib/Support/Unix/Program.inc:561:24: error: use of undeclared identifier '_POSIX_ARG_MAX'
```
posix says this should go in limits.h and have a value of `4096`.  We should put this in:

libc/include/llvm-libc-macros/limits-macros.h
</pre>
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