I used the windows development evaluation vm and once the tools setup, I ran inside a vs native development console the following:
C:\Users\User\Documents\Test\build>cmake -G Ninja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ .. -- The C compiler identification is Clang 12.0.0 with GNU-like command-line -- The CXX compiler identification is Clang 12.0.0 with GNU-like command-line -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Check for working C compiler: c:/Program Files/LLVM/bin/clang.exe - skipped -- Detecting C compile features -- Detecting C compile features - done -- Detecting CXX compiler ABI info -- Detecting CXX compiler ABI info - done -- Check for working CXX compiler: c:/Program Files/LLVM/bin/clang++.exe - skipped -- Detecting CXX compile features -- Detecting CXX compile features - done -- Configuring done -- Generating done -- Build files have been written to: C:/Users/User/Documents/Test/build
There must be something causing the failure on your setup.
Are you sure, you used the development environment command prompt ?
If it still fails, could you send the output of the command:
cmake -G Ninja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ --trace ..