/usr/lib/ocaml/llvm-3.5/libLLVMExecutionEngine.a is in libllvm-3.5-ocaml-dev 1:3.5.2-3ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ocaml/llvm-3.5/../../llvm-3.5/lib/libLLVMExecutionEngine.a