How to use ObjC in Swift Package Manager

Issue #575

Create Objc target

• http://ankit.im/swift/2016/05/21/creating-objc-cpp-packages-with-swift-package-manager/

Check runtime

Check for example _runtime(_ObjC) or os(macOS if you plan to use platform specific feature

• https://github.com/Quick/Quick/blob/master/Package.swift
• https://github.com/Quick/Quick/pull/687/files

For example, in test we use XCTest which is run via Xcode and is a macOS framework, so we need to check for os(macOS)

Note that in Objc framework, the header files must be in include folder

targets: {
        var targets: [Target] = [
            .testTarget(
                name: "QuickTests",
                dependencies: [ "Quick", "Nimble" ],
                exclude: [
                    "QuickAfterSuiteTests/AfterSuiteTests+ObjC.m",
                    "QuickFocusedTests/FocusedTests+ObjC.m",
                    "QuickTests/FunctionalTests/ObjC",
                    "QuickTests/Helpers/QCKSpecRunner.h",
                    "QuickTests/Helpers/QCKSpecRunner.m",
                    "QuickTests/Helpers/QuickTestsBridgingHeader.h",
                    "QuickTests/QuickConfigurationTests.m",
                ]
            ),
        ]
#if os(macOS)
        targets.append(contentsOf: [
            .target(name: "QuickSpecBase", dependencies: []),
            .target(name: "Quick", dependencies: [ "QuickSpecBase" ]),
        ])
#else
        targets.append(contentsOf: [
            .target(name: "Quick", dependencies: []),
        ])
#endif
        return targets
    }(),