Add missing System sources to CMake build

[fallintoplace]

Summary

This updates the CMake source list for SystemPackage so it matches the Swift sources in the SwiftPM target.

The CMake build now includes the previously omitted source groups:

• Windows support files
• temporary-path implementation files
• FileSystem APIs, including Stat, FileType, FileMode, and FileFlags
• Linux-only IORing files

It also enables the Swift Lifetimes feature for the CMake target, matching SwiftPM, so the Linux IORing sources are not compiled away when they are included.

Why

The CMake target had drifted from the SwiftPM target. CMake consumers could get a successful build while the produced module was missing newer API areas.

Validation

• cmake configure with Ninja and CMAKE_INSTALL_PREFIX=.build/install-system-sources-check
• cmake --build .build/cmake-system-sources-check
• cmake --install .build/cmake-system-sources-check
• Installed-module Swift typecheck that imports SystemPackage and uses FilePath.stat() / Stat.type
• Source-list audit: CMake now names 40/40 Swift sources from the SwiftPM target

[jrflat]

LGTM, thanks! I verified locally on macOS/Linux, but I'll also trigger cross-repo CI that exercises the CMake path to confirm before merging