libctf AC_CANONICAL_TARGET

AC_CANONICAL_TARGET is needed for @target@ substitution in the
makefile.  AC_CANONICAL_HOST and AC_CANONICAL_BUILD are alread invoked
indirectly, make them explicit.

	* configure.ac: Invoke AC_CANONICAL_TARGET, AC_CANONICAL_HOST
	and AC_CANONICAL_BUILD.
	* configure: Regenerate.
	* Makefile.in: Regenerate.