[CMake] Remove conditional source file lists in WTF
https://bugs.webkit.org/show_bug.cgi?id=114250

Reviewed by Laszlo Gombos.

Use the #ifdef in the source file instead of conditional adding
files to the list of source files. This allows us to remove the
information of enabled features from CMake in next step.

* wtf/CMakeLists.txt:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148004 268f45cc-cd09-0410-ab3c-d52691b4dbfc