fix infinite loop in D.Client.TargetSelector

The pattern guard was clearly meant as a list-comprehension filter,
but on a let-bound pattern, it instead caused a circular loop in which
whether the LHS variables are bound the the RHS values depends on the
values of the LHS variables.

fixes #5081

cabal-install/Distribution/Client/TargetSelector.hs

@@ -611,8 +611,9 @@ disambiguateTargetSelectors matcher matchInput exactMatch matchResults =
             Left  ( originalMatch
                   , [ (forgetFileStatus rendering, matches)
                     | rendering <- matchRenderings
-                    , let (Match m _ matches) | m /= Inexact =
+                    , let Match m _ matches =
                             memoisedMatches Map.! rendering
+                    , m /= Inexact
                     ] )
 
       | (originalMatch, matchRenderings) <- matchResultsRenderings ]