Split clone value and instruction in the echo C API test

Summary: This is a bit of refactoring required to be able to generate instruction in forward basic block. This, for instance, is a requirement for phi in loops.

Reviewers: bogner, chandlerc, echristo, dblaikie, joker.eph, Wallbraker

Differential Revision: http://reviews.llvm.org/D17050

llvm-svn: 260324