flatbuffers: Uprev to 2.0.0

Uprev dev-libs/flatbuffers to version 2.0.0.

This will allow using new features, like optional scalars, in Chrome OS
code. This also pulls a few bugfixes.

This change adds a subslot for the package, so that depending packages
that were built against 1.* get rebuilt after the uprev.

TEST=emerge-$BOARD cryptohome libtextclassifier tensorflow

Cq-Depend: chromium:3110412,chromium:3141476,chrome-internal:4112270
Change-Id: I349afc6f2eee429ef93382ca2711a154c5129c4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/3105985
Tested-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Allen Webb <allenwebb@google.com>
Commit-Queue: Maksim Ivanov <emaxx@chromium.org>
2 files changed