Linux build fixes

define WORKQ_ADDTHREADS_OPTION_OVERCOMMIT for DISPATCH_USE_INTERNAL_WORKQUEUE
remove unused _swift_dispatch_apply_current_root_queue symbol
remove duplicate _dispatch_adopt_wlh_anon() in _dispatch_mgr_thread(), this is already set by its caller _dispatch_root_queue_drain()

Signed-off-by: Daniel A. Steffen <dsteffen@apple.com>
6 files changed