[OCaml] Add REQUIRES: native, object-emission to the Target test

While the test would work with any compiled in target with object
emission support, it's nontrivial to formulate this condition in
lit, so a conservative restriction is used instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194781 91177308-0d34-0410-b5e6-96231b3b80d8