Don't ignore goal order parameter when generating summarized solver log.

After haskell#5012, the solver generated the summarized log by using a goal order that
preferred goals from the final conflict set.  It completely ignored the original
goal order parameter.  This caused a failure in one of the unit tests that set a
goal order and then checked the summarized log, when the solver's goal order
changed for other reasons (See haskell#5012).

This commit combines the two goal orders, with the goal order that prefers goals
from the conflict set taking precedence over the original goal order.

cabal-install/Distribution/Solver/Modular.hs

@@ -9,6 +9,9 @@ module Distribution.Solver.Modular
 -- and finally, we have to convert back the resulting install
 -- plan.
 
+import Prelude ()
+import Distribution.Client.Compat.Prelude
+
 import Data.Map (Map)
 import qualified Data.Map as M
 import Data.Set (Set)
@@ -143,9 +146,14 @@ solve' sc cinfo idx pkgConfigDB pprefs gcs pns =
     rerunSolverForErrorMsg :: ConflictSet -> String -> String
     rerunSolverForErrorMsg cs finalMsg =
       let sc' = sc {
-                    goalOrder = Just (preferGoalsFromConflictSet cs)
+                    goalOrder = Just goalOrder'
                   , maxBackjumps = Just 0
                   }
+
+          -- Preferring goals from the conflict set takes precedence over the
+          -- original goal order.
+          goalOrder' = preferGoalsFromConflictSet cs <> fromMaybe mempty (goalOrder sc)
+
       in unlines ("Could not resolve dependencies:" : messages (runSolver sc'))
           ++ finalMsg