Handle target.bionic in bp2build.

Soong supports some hand-crafted target.<type> that match multiple os or
arch types to simplify configuring for similar targets. target.bionic is
used to match on both android and linux_bionic OSes for cases where they
should be handled the same way.

Test: build/bazel/ci/bp2build.sh
Change-Id: I47b6aaf3279e4d242c4fd0e12f24117eb98e0665