Make sure a out/build_number.txt file is present with linux-bionic

On some branches if out/build_number.txt must be present for
linux_bionic targets to be built. This makes the build_linux_bionic.sh
script create this file.

Test: DIST_DIR=$PWD/fast-out/dist ./art/tools/dist_linux_bionic.sh showcommands com.android.runtime.host com.android.support.apexer
Bug: 132822173
Change-Id: Idc2e89e3947468f26d61d2db224910f3c13410d7
1 file changed