INTERP_STATS macro is bitrotted (slightly)

Turning on the INTERP_STATS macro leads to some compiler errors. You also have to add additional instrumentation at start-up and shutdown to get the stats to be printed.

If you toggle this macro, things should compile and it should print out stats without additional work.

added needs triage label

mentioned in commit 50ba8301

mentioned in merge request !13879 (closed)

assigned to @mpickering

added GHCi RTS Tbug profiling labels and removed needs triage label

added Pnormal label

mentioned in commit fd9c9f7f

closed with commit 66c7f656

mentioned in commit 66c7f656