Implement CPU feature detection for ARM Linux.

webrtc/system_wrappers/cpu_features_webrtc.gyp

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 {
   'conditions': [
     ['OS=="android"', {
       'targets': [
         {
           'target_name': 'cpu_features_android',
           'type': 'static_library',
           'sources': [
             'source/cpu_features_android.c',
           ],
           'dependencies': [
             '../../build/android/ndk.gyp:cpu_features',
           ],
         },
       ],
     }],
+    ['OS=="linux"', {
+      'targets': [
+        {
+          'target_name': 'cpu_features_linux',
+          'type': 'static_library',
+          'sources': [
+            'source/cpu_features_linux.c',
+          ],
+          'dependencies': [
+            '<(webrtc_root)/common.gyp:webrtc_common',
+          ],
+        },
+      ],
+    }],
   ], # conditions
 }