Add an ISA argument to dfg.display_inst().

Include ISA-specific annotations in tracing and error messages.

lib/cretonne/src/binemit/mod.rs

@@ -53,5 +53,5 @@ pub trait CodeSink {
 pub fn bad_encoding(func: &Function, inst: Inst) -> ! {
     panic!("Bad encoding {} for {}",
            func.encodings[inst],
-           func.dfg.display_inst(inst));
+           func.dfg.display_inst(inst, None));
 }

lib/cretonne/src/binemit/relaxation.rs

@@ -135,7 +135,7 @@ fn relax_branch(dfg: &mut DataFlowGraph,
     let inst = pos.current_inst().unwrap();
     dbg!("Relaxing [{}] {} for {:#x}-{:#x} range",
          encinfo.display(encodings[inst]),
-         dfg.display_inst(inst),
+         dfg.display_inst(inst, None),
          offset,
          dest_offset);
     unimplemented!();