Implement CPU feature detection for ARM Linux.

webrtc/system_wrappers/cpu_features_webrtc.gyp

Index: webrtc/system_wrappers/cpu_features_webrtc.gyp
diff --git a/webrtc/system_wrappers/cpu_features_webrtc.gyp b/webrtc/system_wrappers/cpu_features_webrtc.gyp
index 064b3cf049c116e5efd918a53a8f41882f7dbbe0..dd870cf746640b7a78789772606de8421de9734c 100644
--- a/webrtc/system_wrappers/cpu_features_webrtc.gyp
+++ b/webrtc/system_wrappers/cpu_features_webrtc.gyp
@@ -22,5 +22,19 @@
         },
       ],
     }],
+    ['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
 }