Multiple permutations into a VM are generated incorrectly

[pacheco]

Currently, linking into a VM submachine with more than two permutations generates the wrong constraints.
As an example, the following permutations are generated for a simple case with two operations (add/sub):

main.instr_add { 2, main.X, main.Y, main.Z } is main_arith.instr_return { main_arith._operation_id, main_arith._input_0, main_arith._input_1, main_arith._output_0 };
main.instr_sub { 4, main.X, main.Y, main.Z } is main_arith.instr_return { main_arith._operation_id, main_arith._input_0, main_arith._input_1, main_arith._output_0 };

RHS selector needs to be unique for the valid rows of each operation.

[pacheco]

maybe we can use a single permutation per caller machine, the discussion in these issues might be useful #1077 #1073