WebCore.framework should restrict allowable_clients

WebCore.framework should restrict allowable_clients
https://bugs.webkit.org/show_bug.cgi?id=171260

Reviewed by Alexey Proskuryakov.

* Configurations/WebCore.xcconfig: Adding allowable_client to all platform, in order to restrict WebCore
from being directly linked on any platform.
Moved WebKitLegacy and WebCoreTestSupport to OTHER_LDFLAGS_BASE.
Removed WebKit2 as allowable_client from mac.
Added iTunesU, Casablanca and Remote to OTHER_LDFLAGS_BASE_ios for iTunes related projects.
Added WebKit, TVBooks, DumpRenderTree, WebKitTestRunner and TestWebKitAPI to OTHER_LDFLAGS_BASE_ios.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@215769 268f45cc-cd09-0410-ab3c-d52691b4dbfc