x265: set CMAKE_HOST_SYSTEM instead of just removing --build.

Inetrestingly, host/build seems inverted in cmake compared
to autotools (and actually matches our build system).


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6108 b64f7644-9d1e-0410-96f1-a4d463321fa5
build: support Xcode 5.1

Unknown compiler options now result in an error,
previous behavior they were simply ignored.


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6109 b64f7644-9d1e-0410-96f1-a4d463321fa5