[GTK] [gyp] Adding support for building WebCore rendering
https://bugs.webkit.org/show_bug.cgi?id=113213

Reviewed by Gustavo Noronha Silva.

* WebCore.gyp/WebCoreGTK.gyp: Build the rendering directory into a shared library.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146798 268f45cc-cd09-0410-ab3c-d52691b4dbfc