shaderc: added package from upstream

Added media-libs/shaderc to version 2020.6_pre20210327 on amd64,
arm

Changed the ebuild to allow python3.6, previously it was
>= 3.7

BUG=b:195262671
TEST=ran emerge, CQ passes

Change-Id: I4079a74fb187e6c6a3e54403651d6c20359ab69f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/3065955
Reviewed-by: Jim Pollock <jmpollock@chromium.org>
Tested-by: Michael Olney <mpolney@google.com>
Commit-Queue: Michael Olney <mpolney@google.com>
5 files changed