llvm-project git build with nix (without runtimes, clangir enabled, using mold as the linker)

llvm.nix

{
  src,
  targets ? "host",
  projects ? "clang;lld;mlir;libc",
  stdenv,
  cmakeMinimal,
  ninja,
  python313,
  mold,
}:
{

  llvm-project = stdenv.mkDerivation {
    name = "llvm-project";
    version = "20.0.0.git";
    src = src;

    cmakeFlags = [
      "-DC_INCLUDE_DIRS=${stdenv.cc.libc.dev}/include"
      "-GNinja"
      "-DCMAKE_BUILD_TYPE=MinSizeRel"
      "-DCMAKE_INSTALL_PREFIX=$out"
      # Reduce installation size by using a single 'llvm' binary with symlinks
      "-DLLVM_TOOL_LLVM_DRIVER_BUILD=ON"
      "-DLLVM_ENABLE_PROJECTS=${projects}"
      "-DLIBC_HDRGEN_ONLY=ON"
      "-DLLVM_LIBC_FULL_BUILD=ON"
      "-DLLVM_TARGETS_TO_BUILD=${targets}"
      "-DCLANG_ENABLE_CIR=ON"
      "-DCLANG_DEFAULT_CXX_STDLIB=libc++"
      "-DCLANG_DEFAULT_UNWINDLIB=libunwind"
      "-DCLANG_DEFAULT_RTLIB=compiler-rt"
      "-DMLIR_ENABLE_SPIRV_CPU_RUNNER=ON"
      "-DMLIR_ENABLE_EXECUTION_ENGINE=ON"
      "-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=all"
      "-DLLVM_USE_LINKER=mold"
      "-S${src}/llvm"
    ];

    nativeBuildInputs = [
      cmakeMinimal
      ninja
      python313
      mold
    ];
  };
}