build: link against swiftOnoneSupport in debug configuration
build: link against swiftOnoneSupport in debug configuration

When building debug, swift requires a supplementary library.  The swift driver
is aware of this and will make the appropriate arrangements.  However, since the
swift component is compacted into the C library, the linker driver being used
does not understand this requirement.  Explicitly link against the support
library.  This allows building the debug configuration of libdispatch with a
release configuration of the swift standard library.

apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch