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/mod.rs

@@ -94,4 +94,8 @@ impl TargetIsa for Isa {
     fn emit_inst(&self, func: &ir::Function, inst: ir::Inst, sink: &mut CodeSink) {
         binemit::emit_inst(func, inst, sink)
     }
+
+    fn reloc_names(&self) -> &'static [&'static str] {
+        &binemit::RELOC_NAMES
+    }
 }