Hi Mike, I’ve just tried myself on my (Sequoia, but clang-1700.6.3.2 and the same CMake version installed through homebrew), using the same setup apart from qt5 that you posted in Rebuilding "everything" after MacOS upgrade?, and the needed patch to g4tools.
I don’t get the misconfiguration of HAVE_TLS. The code that tests this is really just
__thread int i; int main(){return 0;}
so just to check there’s no setup issue, you could try compiling that on the command line just to check the raw compiler (/usr/bin/c++, which should be clang++ under the hood.)accepts it.
It’s just possible this is a CMake caching issue, though that should be stable across switching MT on/off.
I have no idea why it built with x86_64! You could run the build of Geant4 itself again with make VERBOSE=1 to check what -arch flag it’s adding. On mine, I do get a -arch arm64.