[orc-rt] Make Session explicitly immovable. (llvm#167640)

NFCI -- the deleted copy constructor already made this immovable. The
explicit operations just make clear that this was intentional.

Author: lhames

orc-rt/include/orc-rt/Session.h

@@ -42,6 +42,8 @@ class Session {
   // Sessions are not copyable or moveable.
   Session(const Session &) = delete;
   Session &operator=(const Session &) = delete;
+  Session(Session &&) = delete;
+  Session &operator=(Session &&) = delete;
 
   ~Session();