[EFL][CMAKE] Build break after r149259
https://bugs.webkit.org/show_bug.cgi?id=115339

Reviewed by Gyuyoung Kim.

r149259 used c++11 features(Right angle bracket, Range-based for-loop).
This patch enforces c++0x when cmake based ports build WebKit2 using gcc.

* Source/cmake/WebKitHelpers.cmake:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149266 268f45cc-cd09-0410-ab3c-d52691b4dbfc