core: Try to fix the exit hang (#4811)

* add signal removal

* use a flag instead

* remove signals in cleanup

src/Compositor.cpp

@@ -372,6 +372,9 @@ void CCompositor::cleanup() {
     if (!m_sWLDisplay || m_bIsShuttingDown)
         return;
 
+    signal(SIGABRT, SIG_DFL);
+    signal(SIGSEGV, SIG_DFL);
+
     removeLockFile();
 
     m_bIsShuttingDown   = true;