roll clang_linux package to Clang 6

It was released yesterday.

Change-Id: Ied9ef3c65fcee0ac7af785c6642fb899d6bd4b0d
Reviewed-on: https://skia-review.googlesource.com/113380
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed