Straightforward CMake build doesn't work on Mac and no instructions available.

[dabrahams]

Why this matters: I want to submit PRs that make this project more consumable as a dependency of other CMake projects. Without a baseline understanding of what is expected to work, I can't test my changes.

ArgumentParser version: the main branch
Swift version: swift-driver version: 1.87.3 Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)
Target: arm64-apple-macosx14.0

Checklist

• If possible, I've reproduced the issue using the main branch of this package
• I've searched for existing GitHub issues

Steps to Reproduce

cmake -GNinja -S . -B .cmake-build -DBUILD_TESTING=1 -DBUILD_EXAMPLES=1 && 
  cmake --build .cmake-build && 
  ctest -V --test-dir .cmake-build

Expected behavior

Successful build and test.

Actual behavior

/Users/dave/src/swift-project/swift-argument-parser/Sources/ArgumentParserTestHelpers/TestHelpers.swift:14:8: error: no such module 'XCTest'
import XCTest
       ^
/Users/dave/src/swift-project/swift-argument-parser/Sources/ArgumentParserTestHelpers/TestHelpers.swift:14:8: error: no such module 'XCTest'
import XCTest
       ^