Eliminate most uses of the machine instruction vector for each LLVM instr,

Eliminate most uses of the machine instruction vector for each LLVM instr,
since some m. instr. may be generated by LLVM instrs. in other blocks.
Handle non-SSA (anti and output) edges and true edges uniformly by
working with machine instructions alone.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@1269 91177308-0d34-0410-b5e6-96231b3b80d8