hurd: Stop relying on VM_MAX_ADDRESS

hurd: Stop relying on VM_MAX_ADDRESS

We'd like to avoid committing to a specific size of virtual address
space (i.e. the value of VM_AARCH64_T0SZ) on AArch64.  While the current
version of GNU Mach still exports VM_MAX_ADDRESS for compatibility, we
should try to avoid relying on it when we can.  This piece of logic in
_hurdsig_getenv () doesn't actually care about the size of user-
accessible virtual address space, it just wants to preempt faults on any
addresses starting from the value of the P pointer and above.  So, use
(unsigned long int) -1 instead of VM_MAX_ADDRESS.

While at it, change the casts to (unsigned long int) and not just
(long int), since the type of struct hurd_signal_preemptor.{first,last}
is unsigned long int.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Message-ID: <20240323173301.151066-3-bugaevc@gmail.com>