This is FreeBSD 5.3:

===> Building for fam-2.7.0nb5
....
depfile='.deps/mntent_compat.Po' tmpdepfile='.deps/mntent_compat.TPo' \
depmode=gcc3 /bin/sh ../depcomp \
c++ -DHAVE_CONFIG_H -I. -I. -I.. -I../include -DFAM_CONF=\"/usr/pkg/etc/fam.conf\"    -O2 -c -o mntent_compat.o `test -f 'mntent_compat.c++' || echo './'`mntent_compat.c++
mntent_compat.c++: In function `mntent* statfs_to_mntent(statvfs*)':
mntent_compat.c++:150: error: 'struct statvfs' has no member named 'f_mntfromname'
mntent_compat.c++:151: error: 'struct statvfs' has no member named 'f_mntonname'
mntent_compat.c++:152: error: 'struct statvfs' has no member named 'f_fstypename'
mntent_compat.c++: In function `mntent* getmntent(FILE*)':
mntent_compat.c++:180: error: cannot convert `statvfs**' to `statfs**' for argument `1' to `int getmntinfo(statfs**, int)'
gmake[2]: *** [mntent_compat.o] Error 1
gmake[2]: Leaving directory `/usr/home/reed/pkgsrc/sysutils/fam/work/fam-2.7.0/src'


I am away from my office so I'll have to look at this later.
I may send-pr later.

There are patches from the official fam MASTER_SITE "patches/" directory
for FreeBSD.

Jeremy C. Reed