[OCaml] ExecutionEngine package should not depend on interpreter.

Interpreter support was removed in r220957.
[OCaml] META: remove exists_if(toplevel).

ocamlfind ignores the predicates in this case, making the package
unavailable for batch compilation as well.
[OCaml] Run tests twice, with ocamlc and ocamlopt (if available)

ocamlc and ocamlopt expose a distinct set of buildsystem bugs, e.g.
only ocamlc would detect -custom or -dllib-related bugs, and as all
buildbots will have ocamlopt, these bugs will stay hidden.

This change should add no more than 30 seconds of testing time.
[OCaml] Don't build stub libraries twice.

The default Makefile.rules BUILD_ARCHIVE machinery was
unintentionally enabled.
[OCaml] Avoid embedding absolute paths into executables.

Bindings built out-of-tree, e.g. via OPAM, should append
a line to META.llvm like the following:

linkopts = "-cclib -L$libdir -cclib -Wl,-rpath,$libdir"

where $libdir is the lib/ directory where LLVM libraries are
installed.
[OCaml] Fix ocamlc -custom builds when configured as --enable-shared.
[OCaml] Core package should depend on LLVMTransformUtils for LLVMCloneModule.
[OCaml] Initialize local roots prior to raising.

On 4.02, the OCaml unwinder otherwise gets confused and segfaults.
[OCaml] Don't use deprecated non-caml_namespaced functions.