Don't inject `setupBuildInfo` for non-Custom packages

cabal-install/Distribution/Client/Dependency.hs

@@ -527,14 +527,16 @@ addDefaultSetupDependencies defaultSetupDeps params =
                   Just sbi -> Just sbi
                   Nothing -> case defaultSetupDeps srcpkg of
                     Nothing -> Nothing
-                    Just deps -> Just PD.SetupBuildInfo {
+                    Just deps | isCustom -> Just PD.SetupBuildInfo {
                                                 PD.defaultSetupDepends = True,
                                                 PD.setupDepends        = deps
                                             }
+                              | otherwise -> Nothing
             }
           }
         }
       where
+        isCustom = PD.buildType pkgdesc == PD.Custom
         gpkgdesc = packageDescription srcpkg
         pkgdesc  = PD.packageDescription gpkgdesc