Lots of scripts use shflags to manage command-line flags.  These produce tons of shellcheck warnings of a couple forms:

echo "Running ${FLAGS_count} iterations with:"
              ^-- SC2154: FLAGS_count is referenced but not assigned.

if [ ${FLAGS_errors_fatal} -eq ${FLAGS_TRUE} ]; then
                               ^-- SC2086: Double quote to prevent globbing and word splitting.

We should teach shellcheck about FLAGS_TRUE, FLAGS_FALSE, and the various 
DEFINE_* functions that create these FLAGS_NNN variables.

We might be able to use a shellcheck source directive to read the shflags file.  This would get the definitions for FLAGS_TRUE etc, but we'll still need to teach shellcheck the meaning of the DEFINE_* functions.