VM: Add dart_precompiled build target, a standalone VM without the JIT compiler.

tests/standalone/precompilation_dart2js_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Test generating and running a simple precompiled snapshot of this script.
 
 import 'dart:io';
 
 main(List args) {
   if (args.length > 0 && args[0] == "--hello") {
@@ skipping 69 matching lines @@
         [shared, cc_flags, "-o", libname, "precompiled.S"],
         workingDirectory: tmp.path);
     if (result.exitCode != 0) {
       print(result.stdout);
       print(result.stderr);
       throw "Shared library creation failed!";
     }
 
     var ld_library_path = new String.fromEnvironment("LD_LIBRARY_PATH");
     ld_library_path = "${ld_library_path}:${tmp.path}";
-    exec = "${dart_executable}";
+    exec = "${dart_executable}_precompiled";
     args = ["--run-precompiled-snapshot", "ignored_script", "--version"];
     print("LD_LIBRARY_PATH=$ld_library_path $exec ${args.join(' ')}");
     result = Process.runSync(exec, args,
        workingDirectory: tmp.path,
        environment: {"LD_LIBRARY_PATH": ld_library_path});
     if (result.exitCode != 0) {
       print(result.stdout);
       print(result.stderr);
       throw "Precompiled binary failed.";
     }
     print(result.stdout);
     if (!result.stdout.contains("Dart-to-JavaScript compiler")) {
       throw "Precompiled binary output mismatch.";
     }
   } finally {
     tmp?.deleteSync(recursive: true);
   }
 }