Wine asks for userfaultfd with the i386 syscall number on arm64, so it
never gets one and falls back to mprotect and a SIGSEGV per first write,
which under proot is a ptrace stop each time. libblsession hands it the
real userfaultfd and, where Android refuses the PAGEMAP_SCAN ioctl, answers
it from /proc/self/pagemap and UFFDIO_WRITEPROTECT.
