benchmark: allow compare via fine-grained filters

Before this commit, only benchmark targets defined in Makefile could
be used. This commit allows execution of common.js directly and
passing of filter arguments directly, allowing you to run either a
subset of benchmarks or a single specific benchmark for comparison.

benchmark/compare.js

@@ -1,10 +1,12 @@
 var usage = 'node benchmark/compare.js ' +
             '<node-binary1> <node-binary2> ' +
-            '[--html] [--red|-r] [--green|-g]';
+            '[--html] [--red|-r] [--green|-g] ' +
+            '[-- <type> [testFilter]]';
 
 var show = 'both';
 var nodes = [];
 var html = false;
+var benchmarks;
 
 for (var i = 2; i < process.argv.length; i++) {
   var arg = process.argv[i];
@@ -21,8 +23,15 @@ for (var i = 2; i < process.argv.length; i++) {
     case '-h': case '-?': case '--help':
       console.log(usage);
       process.exit(0);
+      break;
+    case '--':
+      benchmarks = [];
+      break;
     default:
-      nodes.push(arg);
+      if (Array.isArray(benchmarks))
+        benchmarks.push(arg);
+      else
+        nodes.push(arg);
       break;
   }
 }
@@ -65,7 +74,11 @@ function run() {
   env.NODE = node;
 
   var out = '';
-  var child = spawn('make', [runBench], { env: env });
+  var child;
+  if (Array.isArray(benchmarks) && benchmarks.length)
+    child = spawn(node, ['benchmark/common.js'].concat(benchmarks), { env: env });
+  else
+    child = spawn('make', [runBench], { env: env });
   child.stdout.setEncoding('utf8');
   child.stdout.on('data', function(c) {
     out += c;