BUILD FIX (r150089): Make WebCoreTestShim build for iOS

* Configurations/WebCoreTestShim.xcconfig: Exclude
WebCoreTestShimLibrary.cpp when building for iOS.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150114 268f45cc-cd09-0410-ab3c-d52691b4dbfc