build: correct passing `-DDEPLOYMENT_ENABLE_LIBDISPATCH`
build: correct passing `-DDEPLOYMENT_ENABLE_LIBDISPATCH`

This was converted to a generator expression but the FoundationXML and
FoundationNetworking modules did not pass the parameter correctly.

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