target-chromium-os-sdk: Add gcc-bin package to SDK

gcc-bin package provides frozen 4.9.2 GCC toolchains which
are needed for packages that can't use latest upstream GCC.

gcc-bin package is already trimmed to remove most of the
files not needed by GCC.

$ qsize gcc-bin
sys-devel/gcc-bin-4.9.2-r1: 8,930 files, 656 non-files, 544,195.980 KiB

BUG=chromium:1095110
TEST=./update_chroot

Change-Id: I771c30bd23176e502776bad29f1daf9b44540e36
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2618721
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
1 file changed