Disable sanitizers with a blacklist.

We think this might be more flexible.  It allows, e.g, function-level blacklisting,
and here an easy one-stop-shop blacklist for all of third_party/externals.

BUG=skia:

CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Debug-ASAN-Trybot
NOTREECHECKS=true

Review URL: https://codereview.chromium.org/1509733003
4 files changed