TSCUtility: deprecate dl*
TSCUtility: deprecate dl*

Mark the dl* helper functions as deprecated.  There currently is a
singular user of these functions - swift-driver.  swift-driver is able
to host the functions for the proper handling of the shared library
loading/unloading and symbol lookup.

apple/swift-tools-support-core,apple/swift-tools-support-core,apple/swift-tools-support-core,apple/swift-tools-support-core