[GTK] OSX linker doesn't understand --whole-archive

[GTK] OSX linker doesn't understand --whole-archive
https://bugs.webkit.org/show_bug.cgi?id=144557

Patch by Philip Chimento <philip.chimento@gmail.com> on 2015-10-12
Reviewed by Martin Robinson.

.:

* Source/cmake/OptionsGTK.cmake: Turn the macro
ADD_WHOLE_ARCHIVE_TO_LIBRARIES into a no-op on Darwin systems,
because XCode's linker doesn't have the --whole-archive option.

Source/WebKit2:

* PlatformGTK.cmake: Link with extra libraries on Darwin, since
we don't have the --whole-archive linker option.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@190909 268f45cc-cd09-0410-ab3c-d52691b4dbfc