libctf: use libtool for link test in configure

The configure check for ELF support in BFD uses the AC_TRY_LINK.  If
libbfd's dependencies change, this macro will need to be updated
manually with explicit additions to LDFLAGS and LIBS.

This patch updates the check to use libtool instead.

ChangeLog:

	* libctf/configure.ac: Use libtool instead.
	* libctf/configure: Regenerated.