Enable -fexperimental-library on Windows CI

Author: wengxt

.github/workflows/check.yml

@@ -110,7 +110,7 @@ jobs:
         with:
           path: fcitx5
           cmake-option: >-
-            -DENABLE_DBUS=Off -DENABLE_X11=Off -DENABLE_WAYLAND=Off -DENABLE_ENCHANT=Off -DENABLE_SERVER=Off -DENABLE_XDGAUTOSTART=Off -DENABLE_LIBUUID=Off -DENABLE_KEYBOARD=Off
+            -DENABLE_DBUS=Off -DENABLE_X11=Off -DENABLE_WAYLAND=Off -DENABLE_ENCHANT=Off -DENABLE_SERVER=Off -DENABLE_XDGAUTOSTART=Off -DENABLE_LIBUUID=Off -DENABLE_KEYBOARD=Off -DCMAKE_CXX_FLAGS=-fexperimental-library
           shell: pwsh
 
       - name: Test