Switch from use_libfuzzer to using_fuzzing_engine. The current build configuration causes AFL based fuzzers to be built with incorrect options. Bug: 770970 Change-Id: I712dd72a0f680df538e98622032cb13f39ed8c63 Reviewed-on: https://chromium-review.googlesource.com/707933 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>