<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/155531>155531</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            regression compiling cmake on macOS due to __hash_memory link errors
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

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

<pre>
    I have bisected a link error I'm getting to https://github.com/llvm/llvm-project/commit/17d05695388128353662fbb80bbb7a13d172b41d.

One commit before that, all is well. Starting with that commit, I get this link error:

```
Undefined symbols for architecture arm64:
 "std::__1::__hash_memory(void const*, unsigned long)", referenced from:
 unsigned long std::__1::__do_string_hash[abi:se210000]<char const*>(char const*, char const*) in libCMakeLib.a[16](cmBinUtilsLinuxELFLinker.cxx.o)
```

This occurs using my own build of Clang (on arm64 macOS 26 beta, and x86_64 macOS 13) then using that to build CMake (and other projects too).

This is similar to https://github.com/llvm/llvm-project/issues/133304 which was closed as a duplicate of https://github.com/llvm/llvm-project/issues/79933 but that was close as "not planned" because basically "linux need to add availability markups to libc++" but my issue is *on macOS*, where such availability markups do exists IIUC.  So I presume this is different.

@philnik777 @ldionne maybe you have some insight here? Thanks.

</pre>
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