error messagebox upon failure to start up dbg

src/plugins/debugger/gdbengine.cpp

@@ -1530,8 +1530,11 @@ bool GdbEngine::startDebugger()
     m_gdbProc.start(q->settings()->m_gdbCmd, gdbArgs);
     m_gdbProc.waitForStarted();
 
-    if (m_gdbProc.state() != QProcess::Running)
+    if (m_gdbProc.state() != QProcess::Running) {
+        QMessageBox::critical(q->mainWindow(), tr("Debugger Startup Failure"),
+                              tr("Cannot start debugger: %1").arg(m_gdbProc.errorString()));
         return false;
+    }
 
     q->showStatusMessage(tr("Gdb Running"));