Add the very basics of Intel 32-bit instruction encodings.

Tabulate the Intel opcode representations and implement an OP() function
which computes the encoding bits.

Implement the single-byte opcode with a reg-reg ModR/M byte.

lib/cretonne/src/isa/intel/enc_tables.rs

@@ -1,10 +1,11 @@
 //! Encoding tables for Intel ISAs.
 
-use ir::InstructionData;
+use ir::{Opcode, InstructionData};
 use ir::types;
 use isa::EncInfo;
 use isa::constraints::*;
 use isa::enc_tables::{Level1Entry, Level2Entry};
 use isa::encoding::RecipeSizing;
+use super::registers::*;
 
 include!(concat!(env!("OUT_DIR"), "/encoding-intel.rs"));