Clean up -force_load and linkage of libswift_runtime.a. Fixes test Interpreter/Union.swift.
Clean up -force_load and linkage of libswift_runtime.a. Fixes test Interpreter/Union.swift.


Swift SVN r8398

apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation