Commands like gmirror, graid3, ... and others which use dlopen() to load
classes from say, /lib/geom, cannot be statically linked completely.
Moreover, those shared objects may require other shared objects (i.e.
for geom, libraries like -lmd, -lcrypto).

The libs_so extension to crunchgen fixes this by allowing some libraries
to be linked in dynamically. This requires that a copy of rtld and the
shared libraries be made available to the crunched binary, and so is not
suitable for all environments. Crunchgen configurations which do not
use the 'libs_so' keyword are unaffected and produce identical binaries
with and without this commit.

Approved by: murray (mentor, in spirit), jhb
In collaboration with: Adrian Steinmann <ast at marabu dot ch>
MFC After: 6 weeks