To figure our whether a large allocation can be grown into the

To figure our whether a large allocation can be grown into the
following page(s) we've been first mquery()ing for it, mmapp()ing
w/o MAP_FIXED if available, and then munmap()ing if there was a
race.  Instead, just try it directly with
mmap(MAP_FIXED | __MAP_NOREPLACE)

tested in snaps for weeks

ok deraadt@