Liblcthw lib can't compile Ex35

I triying to compile thw liblcthw on exercise 35, and I got undefined reference to mergesort and heapsort i alreay try changing the LDFLAGS and LDLIB env variables but I am still unable to compile these function, I tried installing the bsd library again I m still not able to compile I been using FEDORA 28 as unix system.

I stubbed this functions but some people seem to have solved.
How can I link these functions?