autoconf: detect ctf-tools and add ctf to libafs

autoconf: detect ctf-tools and add ctf to libafs

CTF is a reduced form of debug information similar to DWARF and stab. It
describes types and function prototypes. The principal objective of the
format is to shrink the data size as much as possible so that it could
be included in a production environment. MDB, DTrace, and other tools
use CTF debug information to read and display structures correctly.

This commit introduces a new configure option called --with-ctf-tools.
This option can be used to specify an alternative path where the tools
can be found. If the path is not provided, the tools will be searched
in a set of default directories (including $PATH). The CTF debugging
information will only be included if the corresponding --enable-debug /
--enable-debug-kernel is specified.

Note: at the moment, the Solaris kernel module is the only module
benefited by this commit.

Change-Id: If0a584377652a573dd1846eae30d42697af398d0
Reviewed-on: https://gerrit.openafs.org/12680
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>