The amd64 toolchain buildbots for testing gcc/llvm are here:

gcc: https://uberchromegw.corp.google.com/i/chromeos/builders/amd64-gcc-toolchain
llvm: https://uberchromegw.corp.google.com/i/chromeos/builders/amd64-llvm-toolchain

Tests on these buildbots fail frequently with either of
    "Unhandled DevServerException: CrOS auto-update failed for host aaa.bbb.ccc.ddd: has reached AU retry limit."
or
    "Unhandled DevServerException: CrOS auto-update failed for host aaa-bbb-ccc-ddd: No JSON object could be decoded"

For example, see these two runs from 10/12/2016:

-) https://uberchromegw.corp.google.com/i/chromeos/builders/amd64-gcc-toolchain/builds/30
-) https://uberchromegw.corp.google.com/i/chromeos/builders/amd64-llvm-toolchain/builds/29

These errors are the primary cause these builders are red on most days.