In order to do so we need to install the msdosfs headers to the bootstrap
sysroot and avoid includes of kernel headers that may not exist on every
host (e.g. sys/lockmgr.h). This change should allow bootstrapping of makefs
on FreeBSD 11+ as well as Linux and macOS.
For our CheriBSD builds we always bootstrap makefs by setting
LOCAL_XTOOL_DIRS='lib/libnetbsd usr.sbin/makefs' and use the makefs binary
from the build tree to create a bootable disk image.