Reintroduce "[ORC] Introduce EPCGenericRTDyldMemoryManager."

This reintroduces "[ORC] Introduce EPCGenericRTDyldMemoryManager."
(bef55a2b) and "[lli] Add ChildTarget dependence
on OrcTargetProcess library." (7a219d80) which were
reverted in 99951a56 due to bot failures.

The root cause of the bot failures should be fixed by "[ORC] Fix uninitialized
variable." (03710492) and "[ORC] Wait for
handleDisconnect to complete in SimpleRemoteEPC::disconnect."
(320832cc).