* flag-set.cocci: perform the transformation only if the second
argument is a constant
* sd-journal/lookup3.c: skip the cocci completely for this file, since
it's not "ours"
* strjoina.cocci: skip the transformation on the "test_strjoina" test,
since it intentionally tests the "incorrect" expression we're trying to
transform (the same thing was already done in strjoin.cocci)