Fix CMake build for release/1.2

[cthielen]

This PR cherry picks https://github.com/apple/swift-collections/pull/482/commits, which fixes a typo in the CMake build that is blocking swiftlang/swift#83310.

Checklist

• I've read the Contribution Guidelines
• My contributions are licensed under the Swift license.
• I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (if appropriate).
• I've added benchmarks covering new functionality (if appropriate).
• I've verified that my change does not break any existing tests or introduce unexplained benchmark regressions.
• I've updated the documentation if necessary.

[cthielen]

@swift-ci test

[cthielen]

@swift-ci test

[etcwilde]

It doesn't look like the other patch to add the include(PlatformInfo) landed on this branch so we're not running the PlatformInfo code at all and thus we don't have a swiftmodule triple set. We can drop this commit. (drop 4cf344d from the patch set and you should be good to go)