Slightly optimize the is_eq_exact and is_ne_exact instructions
Slightly optimize the is_eq_exact and is_ne_exact instructions

The `cmp_arg()` helper would generate an unnecessary move to the
SUPER_TMP register if the RHS argument was an X register backed by a
CPU register. For example:

    mov x14, x27
    cmp x26, x14

This code can be simplified to:

    cmp x26, x27

bjorng/otp,potatosalad/otp,bjorng/otp,vinoski/otp,vinoski/otp,dumbbell/otp,erlang/otp,dgud/otp,emacsmirror/erlang,potatosalad/otp,emacsmirror/erlang,bjorng/otp,potatosalad/otp,emacsmirror/erlang,dumbbell/otp,potatosalad/otp,bjorng/otp,vinoski/otp,vinoski/otp,potatosalad/otp,erlang/otp,dumbbell/otp,dumbbell/otp,erlang/otp,dgud/otp,vinoski/otp,emacsmirror/erlang,erlang/otp,erlang/otp,dgud/otp,bjorng/otp,dumbbell/otp,bjorng/otp,dgud/otp,potatosalad/otp,erlang/otp,dumbbell/otp,emacsmirror/erlang,emacsmirror/erlang,potatosalad/otp,dumbbell/otp,dumbbell/otp,vinoski/otp,dgud/otp,emacsmirror/erlang,dumbbell/otp,potatosalad/otp,emacsmirror/erlang,bjorng/otp,vinoski/otp,vinoski/otp,bjorng/otp,erlang/otp,dgud/otp,potatosalad/otp,vinoski/otp,dgud/otp,dgud/otp,vinoski/otp,dgud/otp,emacsmirror/erlang,bjorng/otp,emacsmirror/erlang,potatosalad/otp,dgud/otp,erlang/otp,dumbbell/otp,bjorng/otp,erlang/otp,erlang/otp