sal: add comment re: V718 'CreateThread' should not be called from 'DllMain'

Change-Id: I6e444e6c3dd4f5e158fe9b649b97ccb5ca32c3a7

sal/osl/w32/dllentry.c

@@ -306,6 +306,12 @@ BOOL WINAPI DllMain( HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved )
                     // No error check, it works or it does not
                     // Thread should only be started for headless mode, see desktop/win32/source/officeloader.cxx
                     CreateThread( NULL, 0, ParentMonitorThreadProc, (LPVOID)dwParentProcessId, 0, &dwThreadId );
+                    // Note: calling CreateThread in DllMain is discouraged
+                    // but this is only done in the headless mode and in
+                    // that case no other threads should be running at startup
+                    // when sal3.dll is loaded; also there is no
+                    // synchronization with the spawned thread, so there
+                    // does not appear to be a real risk of deadlock here
                 }
             }