Not doing so means the generated .lut.h files don't #include Lookup.h, so they don't build. The EFL builder is currently broken because of this, but I'm not familiar enough with the system to fix it. You can look at JavaScriptCore/GNUMakefile.am, JavaScriptCore/DerivedSources.make, or JavaScriptCore/DerivedSources.pro for an example.
Assigning to gyuyoung.kim@samsung.com and CC'ing leandro@profusion.mobi because they're listed as the builder owners. Unfortunately, I've never worked with them on any WebKit code, so I'm not sure what the best way to get in touch with them is.
Ok, I look into this problem.
In order to include Lookup.h, "-i" argument should be passed to create-hash-table. So, I add the "-i" option when cmake invokes the create_hash_table. http://trac.webkit.org/changeset/86740
Thanks!