Fix ArgumentParser build failure for WASI (WebAssembly System Interface)

[kkebo]

ArgumentParser is very useful for command-line tools that are built for wasm32-unknown-wasi and run on WebAssembly runtimes (e.g., wasmtime, wasmer, WasmKit). However, starting from version 1.6.0, the use of DispatchSemaphore has caused the build for wasm32-unknown-wasi to break.

This PR is intended to fix that issue.

Checks

• wasm32-unknown-wasi: https://github.com/kkebo/swift-format/actions/runs/16027414126/job/45218842188?pr=412
• wasm32-unknown-wasip1-threads: https://github.com/kkebo/swift-format/actions/runs/16027414126/job/45218842190?pr=412

Checklist

• I've added at least one test that validates that my change is working, if appropriate
• I've followed the code style of the rest of the project
• I've read the Contribution Guidelines
• I've updated the documentation if necessary

[natecook1000]

@kkebo, thanks for this fix! Would you be willing to update https://github.com/apple/swift-argument-parser/blob/main/.github/workflows/pull_request.yml to include those WASM build tests? They could be in a wasm-build job, just like cmake-build.

[kkebo]

@natecook1000 That's great! I've added the wasm-build job to pull_request.yml.