findprog-in: Ignore directories. Reported by Frederick Eaton via Dmitry Goncharov in <https://lists.gnu.org/archive/html/bug-gnulib/2020-03/msg00003.html>. * lib/findprog-in.c (find_in_given_path): When the file found is a directory, set errno to EACCES and, during a PATH search, continue searching. * modules/findprog-in (Depends-on): Add sys_stat, stat.