[OCaml] PR22014: OCaml bindings didn't link to libLLVM-*.so with -Wl,--as-needed

Patch by Evangelos Foutras <evangelos@foutrelis.com>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224766 91177308-0d34-0410-b5e6-96231b3b80d8