Attempt to fix the build of WebCore's code generator on CMake based system
https://bugs.webkit.org/show_bug.cgi?id=126271

Reviewed by Sam Weinig.

* CMakeLists.txt:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161206 268f45cc-cd09-0410-ab3c-d52691b4dbfc