Add a regmove instruction.

This will be used to locally change the register locations of values in
order to satisfy instruction constraints.

lib/cretonne/src/ir/builder.rs

@@ -9,6 +9,7 @@ use ir::{Opcode, Type, Inst, Value, Ebb, JumpTable, SigRef, FuncRef, StackSlot,
          MemFlags};
 use ir::immediates::{Imm64, Uimm8, Ieee32, Ieee64, Offset32, Uoffset32};
 use ir::condcodes::{IntCC, FloatCC};
+use isa::RegUnit;
 
 /// Base trait for instruction builders.
 ///