v_new_from() -> v_new_or_dup()
Rename v_dup_or_reuse() for better semantics
v_dup_or_reuse() doesn't reset backend values
v_new_reg() fully clears the out_val::bits union
x86_64 impl_op() uses the RHS type, since LHS has been consumed
Set backend type in v_dup_or_reuse()
v_new_bp() for base pointer stack values
Frontend memory/ownership fixes for backend values

out_flush_volatile() also consumes its value. This fixes the
unused-register claiming code, as the frontend correctly relinquishes
its grasp on the backend values.
Sanity check after expression gen - value retaining
Ignore gen_expr() values in print "gen" methods

Fixes unused result warnings until the gen functions are correctly separated.