build failure using OBJECT library with Xcode generator
See the attached project (borrowed from an older version of https://github.com/dev-cafe/cmake-cookbook/tree/master/chapter-01/recipe-03/cxx-objlib-example). It contains an OBJECT library that is later used to create both a STATIC library and a SHARED library. On Mac, using CMake 3.18.3, this builds correctly with the Unix Makefiles and Ninja generators, but it fails to build with the Xcode generator.