Define filegroups 'linux-x86' and 'darwin' to provide binaries for bazel builds am: b7b30f478c am: 0f55117cec am: af86747bcd am: 1dbe344a09

Original change: https://android-review.googlesource.com/c/platform/prebuilts/build-tools/+/1714160

Change-Id: I17bf833b354d2aa4533b8d711eec5c14add4b332