[OCaml] Add functions for accessing metadata nodes.

Patch by Xinyu Zhuang.

Differential Revision: http://reviews.llvm.org/D19309

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273370 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed