Warn when failing to restore auto-detected tool chains

Change-Id: If9582c35a35322efcd0d1666a6e52a62df98af21
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/projectexplorer/toolchainmanager.cpp

@@ -190,7 +190,11 @@ void ToolChainManager::restoreToolChains()
     }
 
     // Delete all loaded autodetected tool chains that were not rediscovered:
-    qDeleteAll(tcsToCheck);
+    foreach (ToolChain *tc, tcsToCheck) {
+        qWarning() << QString::fromLatin1("ToolChain \"%1\" (%2) dropped since it was not auto-detected again")
+                      .arg(tc->displayName()).arg(tc->id());
+        delete tc;
+    }
 
     // Store manual tool chains
     foreach (ToolChain *tc, tcsToRegister)