Revert "Revert "Upgrade to 5.0.71.48"" DO NOT MERGE

This reverts commit f2e3994fa5148cc3d9946666f0b0596290192b0e,
and updates the x64 makefile properly so it doesn't break that
build.

FPIIM-449

Change-Id: Ib83e35bfbae6af627451c926a9650ec57c045605
(cherry picked from commit 109988c7ccb6f3fd1a58574fa3dfb88beaef6632)
diff --git a/test/optimize_for_size.isolate b/test/optimize_for_size.isolate
index aa7f570..16b9315 100644
--- a/test/optimize_for_size.isolate
+++ b/test/optimize_for_size.isolate
@@ -2,6 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
+  'variables': {
+    'command': [
+      '../tools/run-tests.py',
+    ],
+  },
   'includes': [
     'cctest/cctest.isolate',
     'intl/intl.isolate',