added skslc to BUILD.gn

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4764

Change-Id: I89330cfa4be4d43d9183a8e53b28d6c0061f33e2
Reviewed-on: https://skia-review.googlesource.com/4764
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
1 file changed