[Orc] In the CompileOnDemand layer, wrap module ownership in order to preserve

the module pointer type passed in by the user.

The previous ownership scheme, where the user pointer was always moved into a
std::shared_ptr, breaks if the user passes in a raw pointer.

Discovered while working on the Orc C API, which should be landing shortly.
I expect to include a test-case with that.

llvm-svn: 251273