* Writing out ELF files is close to working but the following needs to
  be examined more closely:
    - ELF files are written with the wrong E_MACHINE value because
      ELFObjectWriter::WriteHeader function does not yet support
      target specific E_MACHINE values.
    - ELF relocation records are incorrect because the function
      ELFObjectWriter::RecordRelocation is hard coded for X86/X86-64.
    - Relocations use 2-byte / 4-byte to terminology in reference to
      the size of the immediate value being changed. The Xilinx
      terminology seems to be (???) 4-byte / 8-byte in reference
      to the number of bytes of instructions that are being changed.
    - BRLID and like instructions are always assumed to use a 4-byte
      immediate value for the relocation and BEQID and like instructions
      are always assumed to use a 2-byte immediate value for the relocation.
      I think this means that conditional branches like BEQID can only
      branch += 32768 bytes (~8192 instructions). We should allow conditional
      branches to use 4-byte relocations but I'm not sure how to do that
      right now.
    - Relocation records for indirect calls are not being generated
      correctly. These should emit and IMM 0 directly before the ORI
      instruction that loads the register (just like when a BRLID
      instruction is used instead of an ORI).

* Code generation seems to work relatively well now but the following
  needs to be examined more closely:
    - The stack layout needs to be examined to make sure it meets
      the standard, especially in regards to var arg functions.
    - The delay slot filler is ad hoc but seems to work. Load and
      store instructions were prevented from being moved to delay
      slots but I'm not sure that is necessary.
    - The processor itineraries are copied from a different backend
      and need to be updated to model the MicroBlaze correctly.
    - Look at the MBlazeGenFastISel.inc stuff and make use of it
      if appropriate.