Add libs needed by iohandler merge to Makefile for FreeBSD

Copied from the Linux case added in r200263.  Discovered by the FreeBSD
buildbot - I tested the branch with cmake.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@200548 91177308-0d34-0410-b5e6-96231b3b80d8