Use libelf from base.

Index: cddl/usr.bin/ctfmerge/Makefile
--- cddl/usr.bin/ctfmerge/Makefile.orig
+++ cddl/usr.bin/ctfmerge/Makefile
@@ -33,9 +33,8 @@ CFLAGS+=	-I${.CURDIR}/../../../sys/cddl/compat/opensol
 		-I${OPENSOLARIS_USR_DISTDIR}/head \
 		-I${OPENSOLARIS_USR_DISTDIR}/tools/ctf/common \
 		-I${OPENSOLARIS_USR_DISTDIR}/tools/ctf/cvt \
-		-I${OPENSOLARIS_SYS_DISTDIR}/uts/common \
-		-I/usr/local/include/elftoolchain
+		-I${OPENSOLARIS_SYS_DISTDIR}/uts/common
 
-LDADD=		-L/usr/local/lib/elftoolchain -lelf -lz -lpthread
+LDADD=		-lelf -lz -lpthread
 
 .include <bsd.prog.mk>