Convert clang-interpreter to ORC JIT API

Summary: This mostly re-uses code from the KaleidoscopeJIT example.

Reviewers: ddunbar, lhames

Reviewed By: lhames

Subscribers: mgrang, alexshap, mgorny, xiaobai, cfe-commits

Differential Revision: https://reviews.llvm.org/D45897

llvm-svn: 333302