Looking at the target architectures and compiler backend architectures, I notice use of both of these names: arm64 and aarch64. Both of them refer to the 64-bit ARM architecture, why the two names?
Apparently, GCC and other folks went with the name aarch64. But Apple went with the arm64 name in their operating systems and compiler backends. So both names got popular, though it seems like aarch64 is the way to go now since Apple has switched to that too.