Ticky's ticker registration is racy

The code generated for registration of ticky-ticky counters is currently racy. Specifically, GHC.StgToCmm.Ticky.registerTickyCtr adds its ticker to the ticky_entry_ctrs linked-list by performing a read-modify-write, which may race with other threads when compiling threaded code. This really ought to rather be an atomic exchange.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information