Android.bp: Ignore unknown warning flags. Clang and Chrome build with different versions of clang which support different warning flags. Ignore unknown warning flags when building in Android. Bug: b:142320172 Change-Id: I35eb424aa5a146fec7dabf9f3aa71bd6dd9d8f50 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2112282 Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Geoff Lang <geofflang@chromium.org>