[ES6] Arrow function syntax. Feature flag for arrow function

[ES6] Arrow function syntax. Feature flag for arrow function
https://bugs.webkit.org/show_bug.cgi?id=145108

Patch by Skachkov Alexandr <gskachkov@gmail.com> on 2015-05-18
Reviewed by Ryosuke Niwa.

Added feature flag ENABLE_ES6_ARROWFUNCTION_SYNTAX for arrow function

Source/JavaScriptCore:

* Configurations/FeatureDefines.xcconfig:

Source/WebCore:

* Configurations/FeatureDefines.xcconfig:

Source/WebKit/mac:

* Configurations/FeatureDefines.xcconfig:

Source/WebKit2:

* Configurations/FeatureDefines.xcconfig:

Source/WTF:

* wtf/FeatureDefines.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@184517 268f45cc-cd09-0410-ab3c-d52691b4dbfc