update Ubuntu14 CT bots to Clang

To run on these older bots, looks like we need to statically link
libstdc++ and libgcc.  Luckily that is straightforward.

Change-Id: If523067df196e943c2ba2f64c52eea0711dbfcbd
Reviewed-on: https://skia-review.googlesource.com/115743
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Ravi Mistry <rmistry@google.com>
21 files changed