<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/86546>86546</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc] remove LIBC_HAS_BUILTIN
        </td>
    </tr>

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

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

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

<pre>
    libc/src/__support/macros/config.h defines LIBC_HAS_BUILTIN. This was necessary to support older compilers that did not support `__has_builtin`.  All of the compilers we support already have this builtin.
https://libc.llvm.org/compiler_support.html

We should remove this preprocessor macro and its usage throughout the codebase. cc @gchatelet 
</pre>
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