disassembler API.  Hooked this up to the ARM target so such tools as Darwin's
otool(1) can now print things like branch targets for example this:
  blx _puts
instead of this:
  blx #-36
And even print the expression encoded in the Mach-O relocation entried for
things like this:
  movt r0, :upper16:((_foo-_bar)+1234)

llvm-svn: 129284