Fix a bug in the binemit file test.

Only emit each instruction once, or the offset computations go all
wrong.

filetests/isa/riscv/binary32.cton

@@ -75,9 +75,11 @@ ebb0:
     [-,%x7]     v140 = iconst.i32 0x12345000            ; bin: 123453b7
     [-,%x16]    v141 = iconst.i32 0xffffffff_fedcb000   ; bin: fedcb837
 
+    jump ebb1
 
     ; Control Transfer Instructions
 
+ebb1:
     ; beq
     br_icmp eq, v1, v2, ebb0            ; bin: Branch(ebb0) 01550063
     ; bne

src/filetest/binemit.rs

@@ -177,8 +177,6 @@ impl SubTest for TestBinEmit {
                                            inst,
                                            func.dfg.display_inst(inst)));
                     }
-                    sink.text.clear();
-                    isa.emit_inst(&func, inst, &mut sink);
                     let have = sink.text.trim();
                     if have != want {
                         return Err(format!("Bad machine code for {}: {}\nWant: {}\nGot:  {}",