Chromium now requires the 10.15 SDK
(https://bugs.chromium.org/p/chromium/issues/detail?id=1023913), which
breaks the CommandBuffer bot because it's trying to compile with XCode
10.3, which provides the 10.14 SDK.
What's worse, due to reasons I don't fully understand, after failing to
compile CommandBuffer due to the dependence on the 10.15 SDK, the ninja
out dir is poisoned for future compiles that don't depend on the 10.15
SDK.
Also includes a code snippet from
https://skia-review.googlesource.com/c/skia/+/264429 to find the xSAN
dylibs.
Change-Id: I3cd7661a5ea984ea6899e7a5e8cf878581538d9e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272736
Reviewed-by: Ben Wagner aka dogben <benjaminwagner@google.com>
998066127e