Logs (example) can have almost 200K lines that resemble

Could not open output file 'exception.h##9452797c23e5282a181f8cb52f3c8e55.gcov'

As far as the coverage looks, these are innocuous.

These 1) are enormous logs, and 2) sometimes lead to post-process timeouts of 30m. Suppressing the output is one step in that direction.