set_matchpathcon_printf(3) on Linux

The text 070800eec78a, as Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.

set flags controlling the operation of matchpathcon or matchpathcon_index and configure the behaviour of validity checking and error displaying