Add the ability to output line numbers, sort of. It is enabled with the intentionally undocumented -p option (similar to -P but reversed sense) and it might be vaguely useful but only prints the line number when the file changes and may not get the line numbers right.

x
x
x1x
x1x
xx
x12x
t16.c:10:1: Wrong number of arguments for macro c; found 1, expected 2
x1x
t16.c:11:1: Wrong number of arguments for macro c; found 0, expected 2
xx
FAILED