Print YJIT compile time in results

How fast YJIT compile is a very important performance
characteristic, we should keep an eye on it.

harness/harness-common.rb

@@ -107,6 +107,9 @@ def return_results(warmup_iterations, bench_iterations)
     puts "outlined_code_size: #{formatted_stats[:outlined_code_size]}"
     puts "code_region_size:   #{formatted_stats[:code_region_size]}"
     puts "yjit_alloc_size:    #{formatted_stats[:yjit_alloc_size]}"
+    if yjit_stats.key?(:compile_time_ns)
+      puts "yjit_compile_time:  %.2fms" % (yjit_stats[:compile_time_ns] / 1_000_000.0).round(2)
+    end
   end
 
   write_json_file(yjit_bench_results)