libbinder_ndk: add __ANDROID_VENDOR__ error

__ANDROID_VNDK__ is not enough, or it never was

Bug: 295996418
Test: N/A
Change-Id: Id004d64f0be9cc459cb9dc8c4f05e3ff631f8133
diff --git a/libs/binder/ndk/stability.cpp b/libs/binder/ndk/stability.cpp
index 7eafb9c..73eb863 100644
--- a/libs/binder/ndk/stability.cpp
+++ b/libs/binder/ndk/stability.cpp
@@ -27,6 +27,10 @@
 #error libbinder_ndk should only be built in a system context
 #endif
 
+#ifdef __ANDROID_VENDOR__
+#error libbinder_ndk should only be built in a system context
+#endif
+
 #ifdef __ANDROID_NDK__
 #error libbinder_ndk should only be built in a system context
 #endif