Building the clangd LSP

I'm running into trouble when trying to build the clangd language server protocol using wasi-sdk on macOS 15.

I'm using the following script:

#!/bin/bash

set -e -o pipefail

export PATH="$HOME/opt/wasi-sdk-27.0-arm64-macos:$PATH"

export WASI_SDK_PATH="$HOME/opt/wasi-sdk-27.0-arm64-macos"
export WASI_TOOLCHAIN_FILE="${WASI_SDK_PATH}/share/cmake/wasi-sdk.cmake"

cd /tmp
rm -rf build-wasm
mkdir -p build-wasm
cd build-wasm

cmake -G "Unix Makefiles" \
    -DCMAKE_TOOLCHAIN_FILE="${WASI_TOOLCHAIN_FILE}" \
    -DCMAKE_SYSROOT="${WASI_SDK_PATH}/share/wasi-sysroot" \
    -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra" \
    -DLLVM_INCLUDE_TESTS=OFF \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX="$HOME/clangd-wasi" \
    -DCMAKE_CXX_FLAGS="-fno-exceptions" \
    -DLLVM_TARGETS_TO_BUILD="WebAssembly" \
    -DLLVM_DEFAULT_TARGET_TRIPLE="wasm32-wasi" \
    ../llvm-project-llvmorg-21.1.3/llvm

make -j8 clangd

When running cmake, I am stuck on the following error:

-- LLVM default target triple: wasm32-wasi
CMake Error at cmake/modules/HandleLLVMOptions.cmake:245 (MESSAGE):
  Unable to determine platform
Call Stack (most recent call first):
  CMakeLists.txt:1086 (include)

Unfortunately, I am not familiar enough with cmake to know what to try next to debug this problem. Any suggestions?

Start by reproducing the supplied CMake invocation, then read cmake/modules/HandleLLVMOptions.cmake around line 245 and the call from CMakeLists.txt:1086. Determine why platform detection fails for the wasm32-wasi configuration and confirm that configuration can proceed far enough to build clangd.