.PATH to ${.CURDIR}/[...]/kern , the "exists" expression will fail for the
form exists(${.CURDIR}/[...]/kern/). This appears to be happening because
make is searching for the argument to "exists" by using .PATH rather than a
relative search, because .PATH and the argument match at the beginning.
Additionally, make appears to consider a path that starts with ${.CURDIR}
as relative, even though it expands to an absolute path.
The reason that most people aren't seeing this problem is that the absolute
paths of /usr/src/sys and /sys are also searched, so as long as the kernel
source can be found in at least one of those places, no problems surface.
This problem was inadvertently introduced on 1 December 2000, with the
addition of the sysvipc modules.
aabafca098