Upgrade argdata and cloudabi-utils to the latest upstream versions.

Version 0.3 of argdata includes an all new reader/writer API that allows
you to stream argdata objects into files, pipes and sockets. Version 0.4
reworks the iterator API to make it easier/safer to duplicate iterators.

Version 0.4 of argdata now depends on max_align_t. This type definition
is not available on older versions of FreeBSD. Add a local patch to use
a locally defined structure instead. This patch can be removed once we
only support versions that do provide this type.

Version 0.25 of cloudabi-utils catches up with the argdata iterator API
changes.

Reviewed by: bapt
Differential Revision: https://reviews.freebsd.org/D11300