Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Different approach to making all compilers happy.

Allow building with clang (which is being really stupid here...).

Iterate rather than use recursion. We can blow out the kernel stack if there
is a long chain of fork(2)s.