Both x86 and arm clang can output for the other architecture, or universal.

Pass `-arch arm64` not `-march`

You can also `clang -arch x86_64 -arch arm64` to build for both at once.

You can even go a step further and run your clang as native from bazel, via `arch -arm64 clang`.

Put it all together and you have: `arch -arm64 clang -arch x86_64 -arch arm64`.

It may seem like I'm joking but I'm not.