'libraries' ensures proper link order.

If you add it to 'ldflags', you'll get something like `gcc -lelf -o a.out program.o` and that will fail when -Wl,--as-needed is in effect (i.e. don't link libraries unless referenced by object files.)

With 'libraries', you get `gcc -o a.out program.o -lelf` and that's the proper link order.