Added code generation framework.

visitors.h: Contains only IR visitor declarations for now.
code_gen.h: Code generation vistor declaration (needs llvm). generation visitor implementation (needs llvm).
instruction_nodes.h: Classes for each type of instruction; this
            enables the visitor to visit each instruction differently and
            corresponds to the sea of nodes paper.
sea_node.h : Moved base Sea IR Node to this separate header.
             Replaced NO_REGISTER with enum (including RETURN_REGISTER) Addded code generation call.
        Set parent region for SignatureNodes.
        Propagate method and class ids in IR generation routine.
        Create InstructionNode subclasses.
*.mk: Updated to support the new files. Fixed some pre-existing formatting.
instruction_tools.h: Fixed double-define of NO_REGISTER to
                     refer to the new enum. Added support for one more instruction in
                    HasRegXX and VRegXX functions.

Change-Id: I7c78f603e41df7bf9da5b77951b8485dd1b49200
11 files changed