Eliminate POSIX

[aciidgh]

The POSIX module in SwiftPM was written before corelibs-foundation was mature enough. This module provided a great value but isn't good in the long term since we want SwiftPM to be as cross-platform as possible.

[aciidgh]

@swift-ci smoke test

[aciidgh]

@swift-ci smoke test linux

[aciidgh]

@swift-ci smoke test linux

[aciidgh]

@swift-ci smoke test linux

[aciidgh]

@swift-ci smoke test linux

[aciidgh]

Dispatch keeps failing with:

15:08:59 <unknown>:0: warning: missing submodule '_SwiftDispatchOverlayShims'
15:08:59 /home/buildnode/jenkins/workspace/swift-package-manager-Linux-smoke-test/swift-corelibs-libdispatch/src/swift/Block.swift:14:8: error: no such module '_SwiftDispatchOverlayShims'
15:08:59 import _SwiftDispatchOverlayShims

[aciidgh]

@swift-ci smoke test linux

[aciidgh]

@swift-ci smoke test linux

[aciidgh]

@swift-ci smoke test linux

[aciidgh]

@swift-ci test

[aciidgh]

Ok, got the full swift test suite to run successfully.

[therealbnut]

@aciidb0mb3r Nice, almost entirely removed the POSIX dependency! 🎉

Sources/swiftpm-manifest-tool/main.swift still contains POSIX.exit (and an import), could that also change to SPMLibc.exit?

After that the only remaining POSIX usage seems to be import enum POSIX.SystemError.