The makefs msdosfs code includes fs/msdosfs/denode.h which directly uses
struct buf from <sys/buf.h> rather than the makefs struct m_buf.
To work around this problem provide a local denode.h that includes
ffs/buf.h and defines buf as an alias for m_buf.
Reviewed By: kib, emaste
Differential Revision: https://reviews.freebsd.org/D28835
ba2cfa80e1