compiler: Don't show ExceptionContext of GhcExceptions

Most GhcExceptions are user-facing errors and therefore the
ExceptionContext has little value. Ideally we would enable
it in the DEBUG compiler but I am leaving this for future work.

compiler/GHC/Utils/Panic.hs

@@ -127,6 +127,10 @@ instance Exception GhcException where
           PlainProgramError str -> ProgramError str
     | otherwise = Nothing
 
+  -- Explicitly omit ExceptionContext since we generally don't
+  -- want backtraces and other context in GHC's user errors.
+  displayException exc = showGhcExceptionUnsafe exc ""
+
 instance Show GhcException where
   showsPrec _ e = showGhcExceptionUnsafe e