/usr/lib/gerris/m4.awk is in gerris-mpi 20110329-dfsg.2-1build2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gerris/../../share/gerris/lib/m4.awk
/usr/lib/gerris/../../share/gerris/lib/m4.awk