[LLVM-C] Expose User::getOperandUse as LLVMGetOperandUse.

Patch by Gabriel Radanne <drupyog@zoho.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215419 91177308-0d34-0410-b5e6-96231b3b80d8
[OCaml] Expose Llvm.get_operand_use.

Patch by Gabriel Radanne <drupyog@zoho.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215420 91177308-0d34-0410-b5e6-96231b3b80d8