Add a product for building linux_bionic in --soong-only mode.

Modelled after the mainline_sdk product.

Test: build/soong/soong_ui.bash --make-mode --soong-only \
        SOONG_ALLOW_MISSING_DEPENDENCIES=true \
        TARGET_PRODUCT=linux_bionic com.android.art.host
Bug: 31559095
Bug: 229123823
Change-Id: I6051d21cc4bae561e987561ddad5f1ec5435c4ca