message: [spirv] Add lowering for std.fdiv, std.frem, std.fsub
  Closes
  COPYBARA_INTEGRATE_REVIEW=https://github.com/tensorflow/mlir/pull/313 from denis0x0D:sandbox/lowering_std_farith
diff: @@ -21,7 +21,10 @@ class BinaryOpPattern<Op src, Op tgt> :
  (tgt $l, $r)>;
  def : BinaryOpPattern<AddFOp, SPV_FAddOp>;
  +def : BinaryOpPattern<DivFOp, SPV_FDivOp>;
  def : BinaryOpPattern<MulFOp, SPV_FMulOp>;
  +def : BinaryOpPattern<RemFOp, SPV_FRemOp>;
  +def : BinaryOpPattern<SubFOp, SPV_FSubOp>;
  // Constant Op
  // TODO(ravishankarm): Handle lowering other constant types.
  