Fix CompilationUnit's UniquePtr usage.

CompilationUnit defined in compiler_ir.h uses UniquePtr with
forward-declared MIRGraph, so the ctor/dtor must be defined
in a compilation unit that actually includes MIRGraph's
definition. Otherwise the build would depend on the order of
includes.

Change-Id: I53096c5f1c975843bad3c375d4ce72a9c0656264
2 files changed