Fix SIGINFO race causing final results to be lost to stderr.

If a SIGINFO comes in after the file is read then the 'siginfo' flag is set to
1 and the next call to show_cnt() (at exit) would print the data to stderr
rather than the expected stdout.

This was found with spamming Poudriere with SIGINFO which caused a 'wc -l'
execution to return no data rather than an expected number.

MFC after: 2 weeks