cmake DSWIFT_CORELIBS_FOUNDATION_HAS_THREADS examples

swiftlang/swift-corelibs-foundation CMakeLists.txt :200 

list(APPEND _Foundation_common_build_flags
        "-DDEPLOYMENT_ENABLE_LIBDISPATCH"
        "-DSWIFT_CORELIBS_FOUNDATION_HAS_THREADS")

swiftlang/swift-corelibs-foundation CMakeLists.txt :250 

list(APPEND _Foundation_swift_build_flags
        "-DSWIFT_CORELIBS_FOUNDATION_HAS_THREADS")