efl: pragma GCC diagnostic doesn't work properly on gcc >= 4.7.1

Seems to be related to this bug:
 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55881

As a workaround, copied the efl macro body and modified it to apply
a static_cast explicitly.

Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>