Command plugins should respect --build-system selection

[owenv]

Command plugins should use the user specified build system when building any dependencies, and if the command plugin requests a build of its own. Supporting the full range of command plugin functionality with the Swift Build backend will take a little more work, but this patch gets the fundamentals wired up

[owenv]

@swift-ci test

[owenv]

@swift-ci test

[owenv]

@swift-ci test

[owenv]

@swift-ci test self-hosted

[cmcgee1024]

This looks good to me. One of the test failures doesn't seem relevant to this change since it doesn't specify a command plugin and the native build system should be use implicitly. Maybe this is a transient failure of some sort.

✘ Test staticLibrary() recorded an issue at StaticBinaryLibrary.swift:20:6: Caught error: posix_spawn error: No such file or directory (2), `["cp", "-R", "-H", "/Users/ec2-user/jenkins/workspace/swift-package-manager-with-xcode-self-hosted-PR-osx-release-toolchain/branch-main/swiftpm/Fixtures/BinaryLibraries/Static", "/var/folders/bb/hcrjxg1s0b96pfst0ymhmp240000gn/T/BinaryLibraries.OgYWFQ/Static"]`

The failure in PackageCommandNativeTests.testCommandPluginBuildingCallbacks with Windows appears to need a couple of pattern match adjustments to pass.

[owenv]

It may have just been CI failing to trigger with the latest changes

@swift-ci test

[owenv]

@swift-ci test

[owenv]

@swift-ci test Windows

[owenv]

@swift-ci test

[owenv]

@swift-ci test

[owenv]

@swift-ci test Windows

[owenv]

@swift-ci test macOS self hosted

[owenv]

Windows had a network issue on the builder

@swift-ci please test Windows

[owenv]

@swift-ci test macOS

[owenv]

@swift-ci test macOS

[owenv]

Windows timed out

@swift-ci test Windows