ANDROID: fix allmodconfig build to use the right toolchain

Without these changes, the user will be prompted for config changes.

Signed-off-by: Will McVicker <willmcvicker@google.com>
Bug: 153934356
Test: BUILD_CONFIG=common/build.config.allmodconfig.aarch64 build/build.sh
Change-Id: Ib9ef72b217d1e0d78edf136cfe560058e3126d18