- Remove Tilmann's custom truncate lowering: it completely hosed over

- Remove Tilmann's custom truncate lowering: it completely hosed over
  DAGcombine's ability to find reasons to remove truncates when they were not
  needed. Consequently, the CellSPU backend would produce correct, but _really
  slow and horrible_, code.

  Replaced with instruction sequences that do the equivalent truncation in
  SPUInstrInfo.td.

- Re-examine how unaligned loads and stores work. Generated unaligned
  load code has been tested on the CellSPU hardware; see the i32operations.c
  and i64operations.c in CodeGen/CellSPU/useful-harnesses.  (While they may be
  toy test code, it does prove that some real world code does compile
  correctly.)

- Fix truncating stores in bug 3193 (note: unpack_df.ll will still make llc
  fault because i64 ult is not yet implemented.)

- Added i64 eq and neq for setcc and select/setcc; started new instruction
  information file for them in SPU64InstrInfo.td. Additional i64 operations
  should be added to this file and not to SPUInstrInfo.td.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61447 91177308-0d34-0410-b5e6-96231b3b80d8