Fix expression parsing (on FreeBSD, at least)

This reverts part of r204112 (Expression: cleanup unused include).
It looks like MCJIT.h is required to force MCJIT to be linked.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@204170 91177308-0d34-0410-b5e6-96231b3b80d8