MFC r226940 (rmh):

MFC r226940 (rmh):

Fix a few gratuitous library dependencies. Some of the ZFS utilities
are linked with libraries they don't use:

 - zinject doesn't use libavl
 - ztest doesn't use libz
 - zdb uses neither libavl nor libz
 - zfs uses neither libbsdxml nor libm, nor libsbuf
 - zpool uses neither libbsdxml nor libm, nor libsbuf

In addition, libzfs needs libm because it uses pow(), however it isn't
linked with -lm.  This went unnoticed because all its users had -lm before.

git-svn-id: svn://svn.freebsd.org/base/stable/9@240959 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f