I get as far as:
In file included from /opt/SB/debug/SurfaceToolbox/DynamicModeler/Logic/FastMarching/gw_core/../gw_maths/GW_Maths.h:13:
/opt/SB/debug/SurfaceToolbox/DynamicModeler/Logic/FastMarching/gw_core/../gw_maths/GW_MathsConfig.h:139:3: error: "Unknown architecture !"
#error "Unknown architecture !"
Now, I am building on MacOS 11.6, with my CMAKE_OSX_DEPLOYMENT_TARGET set to 10.15, but I have done this before (though a while ago) and had no issues. Perhaps I should build with an up to date deployment target version.