<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/139843>139843</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Cannot build LLVM with clang on Windows
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            platform:windows
      </td>
    </tr>

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

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

<pre>
    The system is Windows x64 with MSVC installed.
It is necessary to build LLVM (clang, lld, etc.) with clang and run the test suite.
I have successfully built entire LLVM including clang with MSVC.
Then I'm trying to build a copy of LLVM with this clang.
```
cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DLLVM_ENABLE_PROJECTS=llvm;lld;clang; ...
```
I got bin/c-index-test.exe linking errors:
```
lld-link: error: duplicate symbol: public: …
>>> defined at clangAST.lib(AttrImpl.cpp.obj)
>>> defined at clang.lib(clang.dll)
```
After adding `-DLLVM_BUILD_STATIC=ON` I got 
```
FAILED: bin/c-index-test.exe 
...
lld-link: error: could not open 'libclang_static.lib': no such file or directory
```
After adding `-DLIBCLANG_BUILD_STATIC=ON` I got 
```
CMake Error:
  Running
   'C:/PROGRA~1/CMake/bin/ninja.exe' '-C' 'D:/build' '-t' 'recompact'
  failed with:
   ninja: error: build.ninja:107505: multiple rules generate lib/clang.lib
```
I would appreciate any help to understand what I'm missing.
</pre>
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