Add build-specific defines to os_types.h for the ProjectBuilder stuff. As
near as I can tell ProjectBuilder doesn't actually define __MACOS__ or
__COCOA__ or __PROJECTBUILDER__ or any other obvious thing. This config
actually passes -D__MACOSX__ on the gcc cmd line and switches off that.

The ogg framework should now build 'out of the box'.

svn path=/trunk/ogg/; revision=2290