Add cc library for window flags.

Bug: 314960895
Test: atest FrameworksCoreTests:WindowFlagsTest
Change-Id: I548c9486102197f31f557625aa01f081726c688f

AconfigFlags.bp

@@ -173,6 +173,11 @@ java_aconfig_library {
     defaults: ["framework-minus-apex-aconfig-java-defaults"],
 }
 
+cc_aconfig_library {
+    name: "com.android.window.flags.window-aconfig_flags_c_lib",
+    aconfig_declarations: "com.android.window.flags.window-aconfig",
+}
+
 // DeviceStateManager
 aconfig_declarations {
     name: "android.hardware.devicestate.feature.flags-aconfig",