Add support for annotated disassembly output for X86 and arm.

Per the October 12, 2012 Proposal for annotated disassembly output sent out by
Jim Grosbach this set of changes implements this for X86 and arm.  The llvm-mc
tool now has a -mdis option to produced the marked up disassembly and a couple
of small example test cases have been added.

rdar://11764962

llvm-svn: 166445