Don't recommend 'nix log' unless experimental feature is enabled

This fixes the issue that `nix-build`, without experimental feature
'nix-command' enabled, recommends the experimental CLI `nix log` to view
build logs. Now it'll recommend the stable `nix-store -l` CLI instead.

Fixes #8118

src/libstore/build/derivation-goal.cc

@@ -911,8 +911,15 @@ void DerivationGoal::buildDone()
                     msg += line;
                     msg += "\n";
                 }
-                msg += fmt("For full logs, run '" ANSI_BOLD "nix log %s" ANSI_NORMAL "'.",
-                    worker.store.printStorePath(drvPath));
+                msg += "For full logs, run '" ANSI_BOLD;
+                if (experimentalFeatureSettings.isEnabled(Xp::NixCommand)) {
+                    msg += "nix log";
+                } else {
+                    msg += "nix-store -l";
+                }
+                msg += " ";
+                msg += worker.store.printStorePath(drvPath);
+                msg += ANSI_NORMAL "'.";
             }
 
             if (diskFull)