Mac on aarch64 uses posix_memmap.c os_mmap which doesn't do anything with
the flag MMAP_MAP_32BIT for that build so this condition ends up asserting unless
the mapping ends up in the first 4 gigs worth of addressable space.
Thsi PR changes to call os_mmap with MMAP_MAP_32BIT flag only when the target
is x86-64 or riscv64, and the macro __APPLE__ isn't enabled. The behavior is similar
to what the posix os_mmap does.