ccache: Add per-package flag

BUG=b:308409836
TEST=BOARD=amd64-generic bazel build @portage//target/chromeos-base/featured --@portage//internal/packages/stage2/target/board/chromiumos/chromeos-base/featured:9999_ccache --//bazel/portage:ccache_dir=$HOME/ccache/

Change-Id: I44765ba88a881b8c027f02341619d91a77727a7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/bazel/+/5222020
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Tested-by: Li-Yu Yu <aaronyu@google.com>
Commit-Queue: Li-Yu Yu <aaronyu@google.com>
135 files changed