swift234

[cmake] Work around lto cmake bug in cmake 3.4.0.

http://public.kitware.com/pipermail/cmake-developers/2015-November/026993.html

We check for this in build-script-impl and if you are running such a version,
special flags are passed in to work around the issue. If you do not have this verison of cmake, this change should not affect you in any way.

This will be fixed in cmake 3.4.1.