Fix libc error detection

[Lichtso]

posix_memalign and mprotect did not check for errors.

[Mrmaxmeier]

Note: mprotect might return -EAGAIN/-EINTR in strange edge-cases (lock contention in Linux's memory manager?):
https://elixir.bootlin.com/linux/latest/source/mm/mprotect.c#L541
It'd probably be safe to re-try the call in this case.

[Lichtso]

Note: mprotect might return -EAGAIN/-EINTR in strange edge-cases (lock contention in Linux's memory manager?):
https://elixir.bootlin.com/linux/latest/source/mm/mprotect.c#L541
It'd probably be safe to re-try the call in this case.

Thanks for the hint, I implemented a retry loop (with 3 trys max).