Xcode 2.1 through 4 supported $(CURRENT_ARCH) in a PBXFileReference
'path' value used in the "Link Binary with Libraries" build phase.
CMake uses this to reference object file locations on link lines to
bring in OBJECT library content.  However, Xcode 5 now evaluates the
$(CURRENT_ARCH) reference in this context as "undefined_arch" so the
wrong path is given to the linker.  There seems to be no alternative way
to produce an architecture-specific value in a PBXFileReference.

Fortunately Xcode 5 now also handles link dependencies for paths linked
through OTHER_LDFLAGS.  For Xcode >= 5, move the OBJECT library object
file references from the link build phase to OTHER_LDFLAGS.  We can
still show the object files in the source group listing in either case.