Support for MCJIT
* Link against MCJIT libraries from LLVM
* Amend LLVM_Util to have a debug mode.
* Some incidental movement of BackendLLVM methods from llvm_instance.cpp
  to backendllvm.cpp.
* Some minor changes to LLVM_Util to support MCJIT.
* Moved some non-essential (and unlikely to inline) functions from
  llvm_opt.cpp to other cpp files. This helps reduce the dependencies
  for llvm_ops.cpp, reduce the amount of bitcode to process, and was
  intended to fix some MCJIT issues.

Currently, this code uses ParseBitcodeFile rather than getLazyBitcodeModule
when MCJIT is enabled, since MCJIT appears to have a bug that causes it to
not correctly find the symbols in the module when using lazy deserialization.