Add another warning to the libc++ Android.bp. am: 911760b18e am: 8d025e2a45 am: 8d14d97534

Original change: https://android-review.googlesource.com/c/platform/external/libcxx/+/1804478

Change-Id: I02520eeb0f9c63f2ea297d81c29b14361b33f4c7