fix ARM64 bootimage=true build

This fixes a problem with atomically updating JIT-compiled static
calls to AOT-compiled code.  It turns out there was also a problem
with the 32-bit ARM code as well, but we never hit it because it is
extremely unlikely that a code address can be loaded with a single
immediate load instruction on 32-bit ARM since it can only handle
numbers with 8 significant bits.  I've fixed that as well.