mountlist: only use libmount when specified libmount can propagate device IDs provided by Linux in /proc/self/mountinfo. However there are currently many shared libs dependencies introduced by libmount with associated runtime and virt mem overhead. Therefore don't enable by default. * m4/ls-mntd-fs.m4: Use --with-libmount to enable at build time. Note the ac_cv_lib_libmount_mnt_table_parse_stream cache variable had a typo and so was ineffective, thus there is no backwards compatibility issue.