[EFL] Introduce DEVELOPER_MODE
https://bugs.webkit.org/show_bug.cgi?id=135884

Reviewed by Gyuyoung Kim.

.:

Like GTK port, DEVELOPER_MODE can be good solution for developing, debugging and testing
instead of SHARED_CORE.
SHARED_CORE can reduce link time and memory consumption but it is slightly different
from release binary.

* Source/cmake/OptionsEfl.cmake:
* Source/cmake/WebKitHelpers.cmake:
Moved fvisibility=hidden to OptionsEfl.cmake

Tools:

* Scripts/webkitdirs.pm: Turn on DEVELOPER_MODE for the EFL port.
(generateBuildSystemFromCMakeProject):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@172894 268f45cc-cd09-0410-ab3c-d52691b4dbfc