I found someone mentioned to use such command line to use cmake with vs2019 and llvm toolset:
cmake -G "Visual Studio 2019" -T ClangCL
However, this would use the llvm version, which is 11.0 for now, was installed by the visual studio instanller.
I want to use a new version, thus 12.0, of llvm which I already installed somewhere else but I don't know how to make cmake and vs to use that.
UPDATE:
What I tried to set the compiler via command line:
E:\my_proj>cmake -G "Visual Studio 16 2019" -A x64 -T "ClangCL" -DCMAKE_C_COMPILER="C:\Program Files\LLVM\bin\clang.exe" -DCMAKE_CXX_COMPILER="C:\Program Files\LLVM\bin\clang++.exe" .
-- Selecting Windows SDK version 10.0.18362.0 to target Windows 10.0.19042.
-- The C compiler identification is Clang 11.0.0 with MSVC-like command-line
-- The CXX compiler identification is Clang 11.0.0 with MSVC-like command-line
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Professional/VC/Tools/Llvm/x64/bin/clang-cl.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 (x86)/Microsoft Visual Studio/2019/Professional/VC/Tools/Llvm/x64/bin/clang-cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
As you could see the cmake picked the clang from the vs installed location and ignored the command line.