[CMake] Proper handling of ENABLE_API_TESTS build option

[CMake] Proper handling of ENABLE_API_TESTS build option
https://bugs.webkit.org/show_bug.cgi?id=91221

Patch by Thiago Marcos P. Santos <thiago.santos@intel.com> on 2012-07-13
Reviewed by Rob Buis.

.:

Make the flag reusable across the ports using CMake. We are about to enable the WTF,
WebCore and WebKit 2 API's at Tools/TestWebKitAPI and other ports using CMake can get
it almost for free.

* CMakeLists.txt:
* Source/cmake/OptionsEfl.cmake:
* Source/cmake/WebKitFeatures.cmake:
* Source/cmakeconfig.h.cmake:

Source/WebKit:

Build unit tests only if ENABLE_API_TESTS is set.

* PlatformEfl.cmake:

Source/WebKit2:

Build unit tests only if ENABLE_API_TESTS is set.

* PlatformEfl.cmake:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@122601 268f45cc-cd09-0410-ab3c-d52691b4dbfc