Instruction (PLI) for disassembly only.

According to A8.6.120 PLI (immediate, literal), for example, different
instructions are generated for "pli [pc, #0]" and "pli [pc, #-0"].  The
disassembler solves it by mapping -0 (negative zero) to -1, -1 to -2, ..., etc.

llvm-svn: 97731