[EFL] Enable -Werror for the EFL port

[EFL] Enable -Werror for the EFL port
https://bugs.webkit.org/show_bug.cgi?id=98715

Patch by Laszlo Gombos <l.gombos@samsung.com> on 2012-11-09
Reviewed by Gyuyoung Kim.

Treat all warnings as errors, except the existing warnings in the
current code base ("unused-parameter", "sign-compare" and "switch").

Thanks for Raphael Kubo da Costa for the extra help.

* Source/CMakeLists.txt: Enable warnings as error for all libraries
(except WebKit and WebKit2) for the EFL port.
Other cmake-based ports are welcome to join.

* Source/cmake/WebKitHelpers.cmake: Treat warnings as errors by
default for cmake-based ports when ENABLE_WERROR is set.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@134057 268f45cc-cd09-0410-ab3c-d52691b4dbfc