I think the AArch64 JIT has come far enough that it doesn't have to
be called experimental anymore.
I'm also labeling the x86-64 JIT as x86-64 for consistence with the
AArch64 JIT. This will especially be helpful if we start supporting
AArch64 on macOS, as AArch64 macOS can run both the x86-64 JIT and
the AArch64 JIT depending on whether you enable Rosetta 2.