This patch is the initial patch for the machine level IR serialization. It creates a new library in CodeGen called Serialization.
This patch introduces the 'mir' file extension that is used by the machine level IR files.
This new library adds a new machine function pass that is responsible for printing out the machine level IR in the new
It also adds the functions and a class that allows llc to parse machine level IR. I've adopted a two stage parsing
approach - at first the optional LLVM IR is parsed so that the corresponding LLVM module can be created. Then
the machine level IR will be parsed at a later stage after llc creates the TargetMachine with the target information
from the already parsed module.