On recent versions of HarmonyOS the previous JIT detection does not
appear to work anymore, since the second `mmap` succeeds.
This moves the failure in spidermonkey to a later point, when SM
remaps memory to be writable. On recent versions of HOS I observed
that the `PROT_WRITE` permission was silently ignored by mprotect, which
lead to a crash later on the first attempt to write to the memory
region.
It's not exactly easy to determine if one can write to a memory location
(if mprotect lies to you), but we can use `read` to check if the memory
region is writable (without triggering a segfault), since `read` will
return an error for invalid addresses (which is possible since the
writing is handled in the kernel).
Since this solution does add more unsafe code than before, we only use
this detection on OpenHarmony, although we could use it on more
platforms later if there are other platforms which also may have JIT
forbidden.
Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>

Co-authored-by: Sam <16504129+sagudev@users.noreply.github.com>
Signed-off-by: Jonathan Schwender <55576758+jschwe@users.noreply.github.com>