Describe symptoms of (and the cure for) #12768 in 8.0.2 release notes
GHC 8.0.2 introduced a bugfix involving GeneralizedNewtypeDeriving in 96d45145. This made typechecking of GND-produced code a bit stricter, and an unfortunate side effect of this was that there were a couple of corner-case programs that stopped compiling when transitioning from GHC 8.0.1 to 8.0.2. Since the number of affected programs seems quite small, and since the fix is so straightforward, we opt to simply note this discrepancy in the 8.0.2 release notes. Resolves #12768.