[CMake] cmake 3.5.2 Xcode generator bug

[Paul Smith]

On Fri, 2016-05-20 at 14:34 -0400, Paul Smith wrote:
> Just discovered a bug in the Xcode generator; this works fine with
> Makefile generator (on OSX or Linux) and Visual Studio, but fails on
> Xcode:

Meh.  Looks like this is documented in add_library():

> Some native build systems may not like targets that have only object 
> files, so consider adding at least one real source file to any target 
> that references $<TARGET_OBJECTS:objlib>.

Unfortunately for me, I really have to have all the object files in the
OBJECT library (see my previous email about generating linker map files
based on the contents), and there're no other files to add into the
library.

Sigh.