BuildSystem: effects Darwin platforms only

BuildSystem: effects Darwin platforms only
- fixed Darwin ppc hosted build reversion introduced in r2242.
- fixed Darwin + Xcode in all scenerios to honor --debug option

*** if building from Xcode there is no need to rebuild but you will have
    to close project and reload; xcodeproj has been updated.

*** if building from terminal there *should* be no need to rebuild;
    the first 'make' after an update is expected to trigger a reconfigure
    and libhb will rebuild.

git-svn-id: svn://localhost/HandBrake/trunk@2248 b64f7644-9d1e-0410-96f1-a4d463321fa5