You probably need to set the osx architecture flag explicitly on the subordinate cmake. Namely set
https://cmake.org/cmake/help/latest/variable/CMAKE_OSX_ARCHITECTURES.html
In the cmake command line which probably involves adding it to the deps makefile. That will force cmake to choose compiler options
You may also need to set the deployment target sdk to knock you off 11.1
But these are pointers not answers. Hope it helps