[sanitizers] Redirect stdout and stderr to TASK_LOG

At some point cpplint.py became very noisy during a build spewing
a few hundred lines of "Done processing..." even with SILENT=1 in
cmake. This attempts to redirect the stdout of "Done processing" to
the task log along with any errors.

Tested by this with and without SILENT=1 to check things.

Differential Revision: https://reviews.llvm.org/D71402
Reviewed By: eugenis