<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/79647>79647</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc++][std-modules] failed to compile libc++ std modules on Windows
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            libc++
      </td>
    </tr>

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

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

<pre>
    Hi, when building libc++ std modules on Windows libc++ include dirs appear to be missing

(reproducer with clang-scan-deps, but compiling the module directly output the same error)
```
> clang-scan-deps --format=p1689 -- clang -x c++ -c F:\llvm\lib\..\share\libc++\v1\std.cppm -o build\.objs\stdmodules\windows\x64\release\c54d4aa169bc4eb69eed289957de829f\std.cppm.obj -Qunused-arguments -m64 -fvisibi
lity=hidden -fvisibility-inlines-hidden -O3 -std=c++23 -stdlib=libc++ -fno-delayed-template-parsing -DNDEBUG

F:\llvm\lib\..\share\libc++\v1\std.compat.cppm:16:10: fatal error: '__config' file not found
```

```
> clang --version
clang version 18.0.0git (https://github.com/llvm/llvm-project.git 0880742a60e9436e439eaee05bf0c8acf4c48a62)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: F:\llvm\bin
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJycVF2P6yYQ_TXkBRFh8OeDH5L4pu1Lq0qt-rjCMLa5wmABzu7211fYvtt0VbVqJQvkmYGZc-YwIgQ9WoAWFVdUdCexxsn59uLjJJbfT71T7-33GrEbfp3A4n7VRmk7YqN7idgVsSsOUeHZqdVAwM7i37RV7jU8R2grzaoAK-0DFssCwuPocA941iFoOyLaIXo5VlZ7WLxTqwSPX3WcsDTCjiRIYYmCJaRq-jVi6eZFm1RNnOAoIeUAGc07dmtc1ri5gpgBg_fOI9YcWUp6fPsv__I5CyZkcH4WEfFuycq6wYTsMZi84W_QiMR3xC-ouBnzmNOme1TczmdU3MIkPOymIxwVt0eWPFGd5bLMmLid0nTE9V_D7jvYRMXtdScTFbe3MkfFzYMBEdKlsshVLkRWNr3MoS8bAMXqpikqBTVrhqcs6WZMfl7tGkAR4cd1BhsDJnOZYzI8dNC93nkwOr4j3k1aKbAfvmQl2hptIZBvvp84JiEqxLsDHNsNiQDePXWfDNYRBUa8gyIR5sWICGQRPnUek-7H7sv11--eJfB_GXXzIuIGGfFLVqaFIn7Bg4jCHALgF4xY9fIinR30iFiFB20AWxfx4Far_l4e_6gZTMgDfNDO7o7deJhwVp_pmY46YsTqKcYlJHTsjth91HFa-1Q3YvcN7b6RxbuvIOM5naJ1TauciZJCk_MSct6AAKBFP1BZCznkMq9FyT6k_YvwI8QE9K0uX8qcLJIcOiJzeMgjavIgtocLJsUuLui33fWDDVEYA6rTG19_bUev7Sc6TqrlquGNOEGbVbTklHOanaaWQlWrvKhok3HWC1nWdcWLqi9pVuQ5lSfdMspymrGSZbTOqnPF6poWitWq4PVQNiinMAttzin52fnxpENYoa2aMq9ORvRgwja6GHvSBGNplPl247Jfx4ByanSI4c9roo5mG3rPUupQcQ1RkY_31-FBaAMqTat92sC_T77T6k373xqN2H3DFRC7b9D-CAAA__9C5rkX">